Teacher's notes and answers to questions in the book - Hodder Plus ...
Teacher's notes and answers to questions in the book - Hodder Plus ...
Teacher's notes and answers to questions in the book - Hodder Plus ...
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WJEC GCSE Additional Science Teacher’s Notes<br />
1<br />
Develop<strong>in</strong>g scientific<br />
enquiry skills<br />
Scientific enquiry skills need <strong>to</strong> be developed throughout <strong>the</strong> course. The various parts of this<br />
chapter should be referred <strong>to</strong> as <strong>the</strong> course progresses. It does not form a s<strong>in</strong>gle ‘unit’ <strong>to</strong> be worked<br />
through consecutively.<br />
_What is a hypo<strong>the</strong>sis (pages 1–2)________________<br />
Questions<br />
1. For each person, say<br />
a if <strong>the</strong> suggestion qualifies as a scientific hypo<strong>the</strong>sis<br />
Jane <strong>and</strong> Dave’s ideas are hypo<strong>the</strong>ses. Aaron <strong>and</strong> Rebecca have no clear evidence for <strong>the</strong>ir<br />
ideas – <strong>the</strong>y are really only guesses.<br />
b if it does, say whe<strong>the</strong>r you th<strong>in</strong>k it is a good scientific hypo<strong>the</strong>sis.<br />
It might be useful here <strong>to</strong> discuss with <strong>the</strong> class what makes one hypo<strong>the</strong>sis ‘better’ than<br />
ano<strong>the</strong>r. Jane has clear evidence for her hypo<strong>the</strong>sis <strong>and</strong> it would be easy <strong>to</strong> test by<br />
experiment. It is a good hypo<strong>the</strong>sis. Dave’s is not a particularly good hypo<strong>the</strong>sis because<br />
<strong>the</strong> evidence he uses is doubtful. It would be OK if Jane’s mum only ever drank one type of<br />
white w<strong>in</strong>e <strong>and</strong> one type of red, but that is unlikely.<br />
2. Expla<strong>in</strong> <strong>the</strong> differences between a hypo<strong>the</strong>sis, a prediction <strong>and</strong> a <strong>the</strong>ory.<br />
A hypo<strong>the</strong>sis offers an explanation but a prediction does not. A hypo<strong>the</strong>sis has not been<br />
extensively tested, while a <strong>the</strong>ory has been extensively tested <strong>and</strong> has been consistently<br />
supported by experimental evidence.<br />
This question is a good exercise <strong>in</strong> communication skills. It is not sufficient for <strong>the</strong> students<br />
<strong>to</strong> simply expla<strong>in</strong> what a hypo<strong>the</strong>sis, a prediction <strong>and</strong> a <strong>the</strong>ory are – <strong>the</strong>y must compare <strong>the</strong>m<br />
<strong>and</strong> expla<strong>in</strong> <strong>the</strong> differences.<br />
_How do you devise a hypo<strong>the</strong>sis (pages 2–4)_______<br />
TASK Devis<strong>in</strong>g a hypo<strong>the</strong>sis (page 4)<br />
1. Suggest at least two possible hypo<strong>the</strong>ses that might expla<strong>in</strong> Pr<strong>in</strong>ce’s behaviour.<br />
Possible hypo<strong>the</strong>sese are:<br />
1) Pr<strong>in</strong>ce can smell his owner approach<strong>in</strong>g from a long distance away.<br />
2) Pr<strong>in</strong>ce hears <strong>the</strong> car when it is some distance away <strong>and</strong> can tell his owner’s car from<br />
o<strong>the</strong>rs.<br />
3) Pr<strong>in</strong>ce’s biorhythm means he can roughly ‘tell <strong>the</strong> time’, <strong>and</strong> he has learnt that his owner<br />
comes home at a certa<strong>in</strong> time each day.<br />
1
WJEC GCSE Additional Science Teacher’s Notes<br />
2. Pick one of your hypo<strong>the</strong>ses <strong>and</strong> suggest how you might test it.<br />
Hypo<strong>the</strong>sis 1 could be tested by flood<strong>in</strong>g <strong>the</strong> room with strong-smell<strong>in</strong>g air freshener <strong>to</strong><br />
‘mask’ <strong>the</strong> detection of <strong>the</strong> owner’s smell, <strong>and</strong> see if Pr<strong>in</strong>ce still goes <strong>to</strong> <strong>the</strong> w<strong>in</strong>dow (it<br />
would be difficult <strong>to</strong> be certa<strong>in</strong> if <strong>the</strong> mask<strong>in</strong>g works, however). Hypo<strong>the</strong>sis 2 could be<br />
tested by gett<strong>in</strong>g <strong>the</strong> owner <strong>to</strong> drive home <strong>in</strong> a different car, <strong>and</strong> see if Pr<strong>in</strong>ce still goes <strong>to</strong> <strong>the</strong><br />
w<strong>in</strong>dow. Hypo<strong>the</strong>sis 3 is easy <strong>to</strong> test if <strong>the</strong> owner arrives home significantly earlier or later<br />
than normal. If Pr<strong>in</strong>ce still goes <strong>to</strong> <strong>the</strong> w<strong>in</strong>dow just before his arrival <strong>in</strong> those circumstances,<br />
it is clearly not related <strong>to</strong> <strong>the</strong> time.<br />
_Draw<strong>in</strong>g conclusions – is my hypo<strong>the</strong>sis supported__<br />
(pages 5–7)<br />
Questions<br />
3. Natalie had a hypo<strong>the</strong>sis that wet paper could hold less weight than dry paper. She tested paper bags,<br />
add<strong>in</strong>g weight 10 g at a time until <strong>the</strong> bag broke. She tested 10 dry bags, <strong>and</strong> <strong>the</strong>n soaked 10 similar<br />
bags <strong>in</strong> water <strong>and</strong> tested <strong>the</strong>m. In every s<strong>in</strong>gle case, <strong>the</strong> wet bags broke with less weight <strong>in</strong> <strong>the</strong>m than<br />
<strong>the</strong> dry bags. What should Natalie’s conclusion be<br />
The correct answer is b Her hypo<strong>the</strong>sis is supported.<br />
4. Glyn had a hypo<strong>the</strong>sis that a certa<strong>in</strong> br<strong>and</strong> of <strong>in</strong>sulated mug did not actually keep dr<strong>in</strong>ks any warmer<br />
than a normal ceramic mug. He timed how long it <strong>to</strong>ok water <strong>to</strong> cool by 10 °C <strong>in</strong> <strong>the</strong> two types of mug.<br />
He ran <strong>the</strong> test 50 times. On average, <strong>the</strong> water <strong>to</strong>ok 6 m<strong>in</strong>utes longer <strong>to</strong> cool down <strong>in</strong> <strong>the</strong> <strong>in</strong>sulated<br />
mug, <strong>and</strong> <strong>in</strong> all 50 tests <strong>the</strong> water <strong>in</strong> <strong>the</strong> ceramic mug cooled quicker. What should Glyn’s conclusion<br />
be<br />
The correct answer is d His hypo<strong>the</strong>sis should be rejected.<br />
TASK Can people tell <strong>the</strong> difference between butter <strong>and</strong> a<br />
butter spread (page 7)<br />
This is a difficult exercise. It has <strong>to</strong> be difficult because <strong>the</strong> aim is <strong>to</strong> test if pupils can draw<br />
appropriate conclusions from ‘real’ science results, which are very often not completely ‘black<br />
<strong>and</strong> white’. There would be little po<strong>in</strong>t giv<strong>in</strong>g pupils data that very clearly supported or<br />
contradicted a hypo<strong>the</strong>sis.<br />
1. Patrick <strong>and</strong> Isobel’s hypo<strong>the</strong>sis was ‘People cannot tell butter spread from butter’. The alternative is<br />
‘People can tell butter spread from butter’. Comment on <strong>the</strong> evidence for each of <strong>the</strong>se hypo<strong>the</strong>ses.<br />
‘People cannot tell butter spread from butter’ – Pure guesswork would lead <strong>to</strong> roughly 50%<br />
success. Although <strong>the</strong>re is a 56% success rate here, <strong>the</strong> difference from 50% is not big<br />
enough <strong>to</strong> reject <strong>the</strong> hypo<strong>the</strong>sis, but it is not supported by this evidence.<br />
‘People can tell butter spread from butter’ – despite <strong>the</strong> 56% success rate, <strong>the</strong> difference is<br />
not big enough <strong>to</strong> clearly support this hypo<strong>the</strong>sis. In addition, <strong>the</strong> results are quite variable<br />
from person <strong>to</strong> person. There is weak evidential support, but overall <strong>the</strong> results are<br />
<strong>in</strong>conclusive.<br />
2. What is your conclusion from <strong>the</strong>se results<br />
The results do not support Patrick <strong>and</strong> Isobel’s hypo<strong>the</strong>sis, but <strong>the</strong> evidence is <strong>to</strong>o weak <strong>to</strong><br />
reject it.<br />
2
WJEC GCSE Additional Science Teacher’s Notes<br />
_ How do scientists evaluate <strong>the</strong>ir methods_________<br />
(pages 8–10)<br />
Question<br />
5. In <strong>the</strong> experiment described at <strong>the</strong> bot<strong>to</strong>m of page 9, how many read<strong>in</strong>gs do you th<strong>in</strong>k <strong>the</strong> person do<strong>in</strong>g<br />
<strong>the</strong> experiment should have taken<br />
20–30 read<strong>in</strong>gs should have been taken. Accept 20, 30 or anyth<strong>in</strong>g <strong>in</strong> between.<br />
TASK Are you a scientist yet (page 10)<br />
Possible hypo<strong>the</strong>ses are:<br />
Woodlice tend <strong>to</strong> be found <strong>in</strong> dark places.<br />
Woodlice move away from <strong>the</strong> light.<br />
Woodlice move more <strong>in</strong> <strong>the</strong> light than <strong>in</strong> <strong>the</strong> dark.<br />
It is very important that people notice warn<strong>in</strong>g signs. Warn<strong>in</strong>g signs are nearly always red.<br />
The colour red is more noticeable than o<strong>the</strong>r colours.<br />
Cheap br<strong>and</strong>s of fizzy dr<strong>in</strong>ks seem <strong>to</strong> go ‘flat’ quicker than more expensive br<strong>and</strong>s.<br />
Cheap dr<strong>in</strong>ks have less carbon dioxide <strong>in</strong> <strong>the</strong>m than expensive ones.<br />
The bottles of cheap dr<strong>in</strong>ks are less air tight than expensive br<strong>and</strong>s.<br />
3
WJEC GCSE Additional Science Teacher’s Notes<br />
2<br />
Cells <strong>and</strong> cell processes<br />
_What are cells (pages 12–13)___________________<br />
Note that <strong>the</strong> structure of <strong>the</strong> electron microscope does not need <strong>to</strong> be learnt.<br />
_Are cells <strong>the</strong> same <strong>in</strong> plants <strong>and</strong> animals___________<br />
(pages 13–15)<br />
PRACTICAL Can you f<strong>in</strong>d cells (page 15)<br />
Note that sampl<strong>in</strong>g your own cheek cells is perfectly acceptable on health <strong>and</strong> safety grounds.<br />
Long ago, when HIV first became a problem, some local authorities asked schools not <strong>to</strong> do<br />
this, but <strong>the</strong> risk is virtually <strong>in</strong>significant <strong>and</strong> <strong>the</strong>re is no reason why this technique should not<br />
be practised.<br />
Pupils should be allowed free <strong>in</strong>vestigation of <strong>the</strong> celery <strong>to</strong> discover what <strong>the</strong>y can. O<strong>the</strong>r<br />
plant material may be added or substituted. Celery is particularly good for look<strong>in</strong>g at xylem<br />
cells, but is not so good for leaf epidermis (Zebr<strong>in</strong>apendula <strong>and</strong> Rhoeo discolour are good for<br />
this).<br />
The specification expects pupils <strong>to</strong> <strong>in</strong>vestigate specialisation of cells. Po<strong>in</strong>t 4 of <strong>the</strong><br />
procedure is <strong>the</strong>refore important, as <strong>the</strong> chapter text does not deal with this. No specific<br />
specialised cells are mentioned <strong>in</strong> <strong>the</strong> specification, so it does not matter which cells <strong>the</strong> pupils<br />
<strong>in</strong>vestigate.<br />
_Can you call viruses liv<strong>in</strong>g organisms (page 16)_____<br />
Question<br />
1. The cell <strong>the</strong>ory says that all liv<strong>in</strong>g organisms are made of cells. Viruses are not made of cells, yet <strong>the</strong><br />
cell <strong>the</strong>ory is still accepted. Suggest why.<br />
Viruses are not considered <strong>to</strong> be fully ‘liv<strong>in</strong>g’ organisms <strong>and</strong> so <strong>the</strong> cell <strong>the</strong>ory does not apply<br />
<strong>to</strong> <strong>the</strong>m.<br />
_How are <strong>the</strong> activities of a cell controlled__________<br />
(pages 17–18)<br />
PRACTICAL What is <strong>the</strong> best temperature <strong>to</strong> wash your<br />
clo<strong>the</strong>s (page 18)<br />
The <strong>answers</strong> <strong>to</strong> <strong>questions</strong> 1–3 depend upon <strong>the</strong> pupil’s experimental design <strong>and</strong> results.<br />
4
WJEC GCSE Additional Science Teacher’s Notes<br />
4. What o<strong>the</strong>r fac<strong>to</strong>rs, apart from <strong>the</strong> effectiveness of sta<strong>in</strong> removal, might <strong>in</strong>fluence a decision about<br />
what temperature <strong>to</strong> use for your wash<br />
High temperatures are more costly because more energy is used; high temperatures cause<br />
some materials <strong>to</strong> shr<strong>in</strong>k.<br />
5. Expla<strong>in</strong> why enzymes allow wash<strong>in</strong>g at a lower temperature than non-biological detergents.<br />
The enzymes catalyse <strong>the</strong> chemical breakdown of <strong>the</strong> sta<strong>in</strong>s. The end products are soluble<br />
<strong>and</strong> so can be removed by water, even at low temperatures. Breakdown of <strong>the</strong> sta<strong>in</strong>s by heat<br />
alone requires higher temperatures.<br />
_ How does <strong>the</strong> nucleus control <strong>the</strong> cell (pages 19–20)<br />
Note that <strong>the</strong> specification does not require c<strong>and</strong>idates <strong>to</strong> know <strong>the</strong> names of <strong>the</strong> bases <strong>in</strong> DNA,<br />
referr<strong>in</strong>g <strong>to</strong> <strong>the</strong>m only as A, C, G <strong>and</strong> T. The names are given here <strong>in</strong> order <strong>to</strong> <strong>in</strong>dicate WHY <strong>the</strong>y<br />
are called A, C, G <strong>and</strong> T.<br />
TASK Discovery of DNA structure (page 20)<br />
This activity is very important. The discovery of DNA is not covered elsewhere <strong>in</strong> <strong>the</strong> <strong>book</strong> but<br />
is required by <strong>the</strong> specification.<br />
_ How do new cells form (pages 20–23)____________<br />
Questions<br />
2. Cats have 38 chromosomes, dogs have 78 <strong>and</strong> wheat has 42. How many chromosomes would you<br />
expect <strong>to</strong> f<strong>in</strong>d <strong>in</strong>:<br />
a an egg cell of a dog 39<br />
b a kidney cell of a cat 38<br />
c a pollen cell of wheat 21<br />
3. Why would meiosis not work as <strong>the</strong> ‘normal’ method of cell division <strong>in</strong> <strong>the</strong> body<br />
The new cells would only have a half set of chromosomes, <strong>and</strong> fur<strong>the</strong>r divisions would<br />
constantly halve that number.<br />
PRACTICAL Observ<strong>in</strong>g cell division (pages 22–23)<br />
This is quite a complex, but reward<strong>in</strong>g, technique. There are risks associated with both <strong>the</strong> sta<strong>in</strong><br />
<strong>and</strong> hydrochloric acid, <strong>and</strong> ethnoic alcohol <strong>and</strong> ethano-orce<strong>in</strong> are both hazardous chemicals. See<br />
Hazcards 38 <strong>and</strong> 38A.<br />
Ethanoic alcohol is made of 3 parts absolute ethanol <strong>to</strong>1 part glacial ethanoic acid. Mix just<br />
before use, add<strong>in</strong>g <strong>the</strong> acid <strong>to</strong> <strong>the</strong> alcohol. www.practicalbiology.org suggests us<strong>in</strong>g 95%<br />
ethanol <strong>in</strong>stead of absolute, but states that chromosomes may not be as clearly def<strong>in</strong>ed.<br />
5
WJEC GCSE Additional Science Teacher’s Notes<br />
Ethano-orce<strong>in</strong> sta<strong>in</strong> is made by gr<strong>in</strong>d<strong>in</strong>g 1.5 g of solid orce<strong>in</strong> with a pestle <strong>and</strong> mortar. In a<br />
fume cupboard, mix 90 cm 3 of glacial ethanoic acid with 110 cm 3 of distilled water <strong>and</strong> br<strong>in</strong>g <strong>to</strong><br />
<strong>the</strong> boil. Pour <strong>the</strong> boil<strong>in</strong>g mixture over <strong>the</strong> orce<strong>in</strong> <strong>and</strong> stir very thoroughly (still <strong>in</strong> <strong>the</strong> fume<br />
cupboard). Leave overnight, <strong>the</strong>n filter <strong>and</strong> s<strong>to</strong>re <strong>in</strong> a tightly-s<strong>to</strong>ppered dark bottle. An<br />
alternative is lac<strong>to</strong>propionicorce<strong>in</strong> sta<strong>in</strong>.<br />
_Do animals <strong>and</strong> plants grow <strong>in</strong> <strong>the</strong> same way_______<br />
(pages 23–24)<br />
Discussion po<strong>in</strong>ts<br />
1. What are <strong>the</strong> advantages <strong>to</strong> a plant of a branched growth form Why might a compact form be better<br />
for animals<br />
Branched growth allows greater spread for light capture (irrelevant <strong>in</strong> animals). Plants are<br />
sedentary <strong>and</strong> so cannot escape preda<strong>to</strong>rs. A branched form allows parts of <strong>the</strong> plant <strong>to</strong> be<br />
lost/damaged without destroy<strong>in</strong>g <strong>the</strong> whole. Animals have no need of a branched form <strong>and</strong><br />
such a form would <strong>in</strong>hibit movement.<br />
2. Why is be<strong>in</strong>g able <strong>to</strong> grow throughout life a particular advantage <strong>to</strong> plants, <strong>and</strong> why would it not be so<br />
advantageous for animals<br />
This aga<strong>in</strong> could be l<strong>in</strong>ked <strong>to</strong> <strong>the</strong> need <strong>to</strong> re-grow parts eaten by animals. It also ensures <strong>the</strong><br />
best chance of reach<strong>in</strong>g light. Nei<strong>the</strong>r is necessary <strong>in</strong> animals, <strong>and</strong> <strong>in</strong>creas<strong>in</strong>g size would mean<br />
constantly <strong>in</strong>creas<strong>in</strong>g food dem<strong>and</strong>s, as well as mak<strong>in</strong>g it difficult <strong>to</strong> support <strong>the</strong> body <strong>and</strong><br />
possibly <strong>to</strong> feed. Small animals do not have <strong>the</strong> adaptations <strong>to</strong> cope with becom<strong>in</strong>g larger.<br />
Questions<br />
4. Describe <strong>the</strong> pattern shown <strong>in</strong> <strong>the</strong> graph (Figure 2.21).<br />
Growth rate starts very high but decl<strong>in</strong>es rapidly until <strong>the</strong> age of 3–4, <strong>the</strong>n more gradually until<br />
<strong>the</strong> age of 12. Between <strong>the</strong> ages of 12–14 <strong>the</strong> rate <strong>in</strong>creases aga<strong>in</strong>, <strong>the</strong>n decl<strong>in</strong>es steadily until<br />
<strong>the</strong> age of 20.<br />
5. Suggest an explanation for <strong>the</strong> shape of <strong>the</strong> graph between <strong>the</strong> ages of 12 <strong>and</strong> 14.<br />
Puberty occurs <strong>and</strong> this is associated with rapid growth.<br />
_What are stem cells (pages 24–25)_______________<br />
TASK How should we use stem cells, if at all (page 25)<br />
This activity is <strong>in</strong>cluded <strong>to</strong> meet <strong>the</strong> needs of <strong>the</strong> specification, <strong>to</strong> discuss <strong>the</strong> future potential<br />
<strong>and</strong> ethical issues surround<strong>in</strong>g stem cell technology.<br />
6
WJEC GCSE Additional Science Teacher’s Notes<br />
3<br />
Transport <strong>in</strong> <strong>and</strong> out of cells<br />
_What is diffusion (pages 27–29)_________________<br />
Questions<br />
1. Why are oxygen <strong>and</strong> carbon dioxide important <strong>in</strong> liv<strong>in</strong>g th<strong>in</strong>gs<br />
Oxygen is needed for respiration, which provides energy for all liv<strong>in</strong>g processes.<br />
Carbon dioxide <strong>in</strong> animals is a waste material. Build up of CO 2 can affect <strong>the</strong> pH of body fluids<br />
which could prevent enzymes work<strong>in</strong>g. In plants, carbon dioxide is needed for pho<strong>to</strong>syn<strong>the</strong>sis,<br />
so that plants can make food.<br />
2. How good a model do you th<strong>in</strong>k Figure 3.1 is of diffusion Is it <strong>in</strong>accurate <strong>in</strong> any ways<br />
It is not a good model! (Note <strong>the</strong> diagram is not <strong>in</strong>tended as a ‘model’, but just a visual<br />
memory cue.) Diffusion is r<strong>and</strong>om movement. This model suggests a force mov<strong>in</strong>g <strong>the</strong> particle<br />
down <strong>the</strong> gradient.<br />
PRACTICAL ‘Modell<strong>in</strong>g’ diffusion (page 28)<br />
1. The marbles never rema<strong>in</strong> <strong>in</strong> a group, <strong>the</strong>y always spread out. Expla<strong>in</strong> why this happens.<br />
If <strong>the</strong> marbles move <strong>to</strong>wards each o<strong>the</strong>r, <strong>the</strong>y will collide <strong>and</strong> bounce off. If <strong>the</strong>y move away<br />
from each o<strong>the</strong>r, noth<strong>in</strong>g impedes <strong>the</strong>m, <strong>and</strong> <strong>the</strong>y move freely. Thus is it easier for <strong>the</strong><br />
marbles <strong>to</strong> spread out.<br />
This is a good exercise for practis<strong>in</strong>g th<strong>in</strong>k<strong>in</strong>g <strong>and</strong> communication skills. Many pupils<br />
will f<strong>in</strong>d it difficult <strong>to</strong> expla<strong>in</strong> <strong>the</strong> process <strong>the</strong>y see, <strong>and</strong> will certa<strong>in</strong>ly be unable <strong>to</strong> do so<br />
without careful observation <strong>and</strong> <strong>in</strong>tellectual engagement with <strong>the</strong> problem.<br />
2. In what way(s) is this model an <strong>in</strong>accurate way of represent<strong>in</strong>g <strong>the</strong> movement of molecules<br />
<br />
<br />
<br />
Molecules move cont<strong>in</strong>uously.<br />
Marbles can only move <strong>in</strong> one plane (along <strong>the</strong> bench); molecules can move <strong>in</strong> all<br />
planes.<br />
Hitt<strong>in</strong>g <strong>the</strong> bench on ei<strong>the</strong>r side is not r<strong>and</strong>om – it will tend <strong>to</strong> propel <strong>the</strong> marbles<br />
<strong>to</strong>ge<strong>the</strong>r <strong>in</strong>itially.<br />
PRACTICAL How does <strong>the</strong> cell membrane affect<br />
diffusion (page 28)<br />
4. Expla<strong>in</strong> <strong>the</strong> colours that you see <strong>in</strong>side <strong>and</strong> outside <strong>the</strong> visk<strong>in</strong>g tub<strong>in</strong>g after 10 m<strong>in</strong>utes.<br />
There will be a blue-black colour <strong>in</strong>side <strong>the</strong> visk<strong>in</strong>g tub<strong>in</strong>g but not outside. The iod<strong>in</strong>e<br />
molecules have diffused <strong>in</strong> through <strong>the</strong> membrane <strong>to</strong> mix with <strong>the</strong> starch, but <strong>the</strong> starch<br />
moleules have been unable <strong>to</strong> diffuse out.<br />
7
WJEC GCSE Additional Science Teacher’s Notes<br />
_ What is osmosis (pages 29–32)_________________<br />
Questions<br />
3. Here are two <strong>answers</strong> given <strong>in</strong> an exam. Nei<strong>the</strong>r of <strong>the</strong>m got any marks. What is wrong with each of<br />
<strong>the</strong>se <strong>answers</strong><br />
a ‘In osmosis, water travels <strong>in</strong> <strong>the</strong> opposite way from diffusion, that is, from a dilute solution <strong>to</strong> a<br />
concentrated solution.’<br />
There is more water <strong>in</strong> a dilute solution than <strong>in</strong> a concentrated solution, so <strong>the</strong> direction of<br />
water movement <strong>in</strong> osmosis is still down a concentration gradient. (It is best <strong>to</strong> avoid<br />
talk<strong>in</strong>g about a high ‘concentration’ of water, as concentrations should be expressed <strong>in</strong><br />
terms of <strong>the</strong> solute, not <strong>the</strong> solvent.)<br />
b ‘When <strong>the</strong> concentrations <strong>in</strong>side <strong>and</strong> outside a cell are equal, <strong>the</strong> movement of water s<strong>to</strong>ps.’<br />
The movement of water does not s<strong>to</strong>p, it just balances out or ‘reaches an equilibrium’. The<br />
net movement of water s<strong>to</strong>ps.<br />
PRACTICAL Osmosis <strong>in</strong> pota<strong>to</strong>es (pages 31–32)<br />
1. Describe <strong>the</strong> trend seen <strong>in</strong> your results, <strong>and</strong> expla<strong>in</strong> how it was caused.<br />
As <strong>the</strong> concentration of sugar <strong>in</strong>creases, <strong>the</strong> weight <strong>in</strong>crease gets less, <strong>and</strong> eventually<br />
becomes a weight loss, which <strong>the</strong>n <strong>in</strong>creases. It is important <strong>to</strong> refer <strong>to</strong> both <strong>the</strong> decrease<br />
<strong>in</strong> weight ga<strong>in</strong> <strong>and</strong> <strong>the</strong> <strong>in</strong>crease <strong>in</strong> weight loss. This is caused <strong>in</strong>itially by <strong>the</strong> decrease <strong>in</strong><br />
<strong>the</strong> concentration gradient between <strong>the</strong> solution (high water) <strong>and</strong> <strong>the</strong> pota<strong>to</strong> (low water) <strong>and</strong><br />
<strong>the</strong>n by <strong>the</strong> <strong>in</strong>crease <strong>in</strong> concentration gradient between <strong>the</strong> pota<strong>to</strong> (high water) <strong>and</strong> <strong>the</strong><br />
solution (low water).<br />
Expla<strong>in</strong><strong>in</strong>g this is quite a challenge <strong>in</strong> terms of communication skills <strong>and</strong> it is<br />
important <strong>to</strong> know that pupils are expected <strong>to</strong> provide a full <strong>and</strong> clear explanation <strong>to</strong><br />
ga<strong>in</strong> credit.<br />
2. The experiment can also be done by measur<strong>in</strong>g change <strong>in</strong> length of <strong>the</strong> pota<strong>to</strong> cyl<strong>in</strong>ders. Expla<strong>in</strong><br />
why measur<strong>in</strong>g mass is better.<br />
Mass takes account of an <strong>in</strong>crease <strong>in</strong> all dimensions. It would be possible (though unlikely)<br />
for <strong>the</strong> cyl<strong>in</strong>der <strong>to</strong> <strong>in</strong>crease <strong>in</strong> diameter but not length, which would lead <strong>to</strong> <strong>in</strong>accurate<br />
results.<br />
3. Why was it important <strong>to</strong> blot <strong>the</strong> pota<strong>to</strong> cyl<strong>in</strong>ders dry before weigh<strong>in</strong>g <strong>the</strong>m <strong>in</strong> step 9<br />
You don’t want <strong>to</strong> weigh liquid which is not actually <strong>in</strong>side <strong>the</strong> pota<strong>to</strong>. This would lead <strong>to</strong><br />
<strong>in</strong>accurate results.<br />
4. Why were you asked <strong>to</strong> record % change <strong>in</strong> mass <strong>and</strong> plot that <strong>in</strong> <strong>the</strong> graph ra<strong>the</strong>r than just change<br />
<strong>in</strong> mass<br />
The pota<strong>to</strong> cyl<strong>in</strong>ders were identical <strong>in</strong> size but not necessarily <strong>in</strong> mass. % <strong>in</strong>crease takes<br />
account of different start<strong>in</strong>g weights.<br />
8
WJEC GCSE Additional Science Teacher’s Notes<br />
4<br />
Pho<strong>to</strong>syn<strong>the</strong>sis <strong>and</strong><br />
respiration<br />
_How does pho<strong>to</strong>syn<strong>the</strong>sis work (pages 35–37)______<br />
PRACTICAL Investigat<strong>in</strong>g fac<strong>to</strong>rs needed for<br />
pho<strong>to</strong>syn<strong>the</strong>sis (pages 35–37)<br />
Experiment 2 – Show<strong>in</strong>g <strong>the</strong> need for chlorophyll<br />
Variegated geranium (green <strong>and</strong> white) works best for this. O<strong>the</strong>r variegated leaves can be used<br />
but some have thicker cuticles which makes <strong>the</strong> starch test less successful. This type of<br />
variegated geranium is not always easy <strong>to</strong> f<strong>in</strong>d <strong>and</strong> it may be advisable <strong>to</strong> use only a part of a<br />
leaf <strong>in</strong> each group <strong>to</strong> allow <strong>the</strong> plant <strong>to</strong> survive for later use.<br />
1. Why was <strong>the</strong>re no need <strong>to</strong> de-starch <strong>the</strong> leaves used for experiment 2<br />
This test simply discovers <strong>the</strong> ‘normal’ situation <strong>in</strong> a variegated leaf. There is always<br />
chlorophyll <strong>in</strong> <strong>the</strong> green parts of <strong>the</strong> leaf <strong>and</strong> never <strong>in</strong> <strong>the</strong> white parts, so <strong>the</strong> only th<strong>in</strong>g that<br />
is necessary is <strong>to</strong> ensure that pho<strong>to</strong>syn<strong>the</strong>sis has had a chance <strong>to</strong> occur before <strong>the</strong><br />
experiment. All <strong>the</strong> o<strong>the</strong>r experiments <strong>in</strong> this series <strong>in</strong>volve subject<strong>in</strong>g similar leaves <strong>to</strong><br />
vary<strong>in</strong>g conditions over a stated time, <strong>and</strong> so de-starch<strong>in</strong>g is necessary because <strong>the</strong><br />
experimental conditions only operate over a set time span.<br />
2. In experiment 3, why was leaf A put <strong>in</strong> a flask conta<strong>in</strong><strong>in</strong>g water<br />
Leaf A is a control <strong>to</strong> show that <strong>the</strong> effect is caused by <strong>the</strong> absence of carbon dioxide, not by<br />
<strong>the</strong> experimental treatment. Water is used <strong>in</strong>stead of sodium hydroxide so that humidity<br />
levels will be similar <strong>in</strong> <strong>the</strong> two flasks.<br />
Discussion po<strong>in</strong>ts<br />
Sodium hydroxide is very corrosive. Apart from any safety hazard, what disadvantage could this be <strong>in</strong><br />
this experiment How could this disadvantage be reduced or overcome<br />
It could be that <strong>the</strong> sodium hydroxide damages <strong>the</strong> leaf, <strong>and</strong> that as a result <strong>the</strong> leaf does not<br />
pho<strong>to</strong>syn<strong>the</strong>sise. Soda lime could be used as an alternative, with an equal volume of ano<strong>the</strong>r<br />
solid (e.g. marble chips) used <strong>in</strong> <strong>the</strong> control.<br />
_ How can we alter <strong>the</strong> rate of pho<strong>to</strong>syn<strong>the</strong>sis_______<br />
(pages 37–39)<br />
TASK What is <strong>the</strong> effect of <strong>in</strong>creas<strong>in</strong>g light <strong>in</strong>tensity on<br />
<strong>the</strong> rate of pho<strong>to</strong>syn<strong>the</strong>sis (pages 38–39)<br />
This exercise will stretch more able pupils <strong>and</strong> will probably be <strong>to</strong>o complex for lower ability<br />
pupils.<br />
9
WJEC GCSE Additional Science Teacher’s Notes<br />
1. Why do you th<strong>in</strong>k <strong>the</strong> time taken for 50% of <strong>the</strong> leaf discs <strong>to</strong> float was measured <strong>in</strong> seconds ra<strong>the</strong>r<br />
than <strong>in</strong> m<strong>in</strong>utes <strong>and</strong> seconds<br />
It is easier because you don’t have <strong>to</strong> calculate decimal fractions of a m<strong>in</strong>ute. It would be<br />
bad practice <strong>to</strong> just measure <strong>to</strong> <strong>the</strong> nearest m<strong>in</strong>ute (<strong>in</strong>accurate) or <strong>to</strong> record m<strong>in</strong>utes <strong>and</strong><br />
seconds (mixed units).<br />
2. It was felt that measur<strong>in</strong>g <strong>the</strong> time taken for 50% of <strong>the</strong> leaf discs <strong>to</strong> float would provide a more<br />
accurate measure of pho<strong>to</strong>syn<strong>the</strong>sis than wait<strong>in</strong>g for all <strong>the</strong> discs <strong>to</strong> float. Why do you th<strong>in</strong>k this is<br />
If some discs were not viable <strong>the</strong>y may not carry out pho<strong>to</strong>syn<strong>the</strong>sis <strong>and</strong> so would never<br />
float.<br />
3. Do you th<strong>in</strong>k <strong>the</strong> variation <strong>in</strong> <strong>the</strong> results is acceptable <strong>to</strong> draw a conclusion from Expla<strong>in</strong> your<br />
answer.<br />
Probably not. Although <strong>the</strong>re is a clear trend, <strong>the</strong> variation between repeats is often greater<br />
than <strong>the</strong> difference between <strong>the</strong> means at adjacent distances.<br />
4. Do you th<strong>in</strong>k three repeats for this experiment is enough Expla<strong>in</strong> your answer.<br />
No. The repeatability of <strong>the</strong>se results is poor <strong>and</strong> so many more repeats should be done.<br />
5. Do you th<strong>in</strong>k that <strong>the</strong> differences <strong>in</strong> <strong>the</strong> results for <strong>the</strong> different distances are significant Expla<strong>in</strong><br />
your answer.<br />
Probably not, given <strong>the</strong> variation <strong>in</strong> <strong>the</strong> results. Even <strong>the</strong> difference between <strong>the</strong> results at 30<br />
<strong>and</strong> 35 cm may not be significant.<br />
6. What conclusion would you draw from <strong>the</strong>se results<br />
Increas<strong>in</strong>g light <strong>in</strong>tensity may <strong>in</strong>crease <strong>the</strong> rate of pho<strong>to</strong>syn<strong>the</strong>sis, but fur<strong>the</strong>r repeats are<br />
necessary <strong>in</strong> order <strong>to</strong> say for certa<strong>in</strong> whe<strong>the</strong>r this is <strong>the</strong> case.<br />
NOTE: These are real results which illustrate <strong>the</strong> uncerta<strong>in</strong>ty often found <strong>in</strong> experimental data.<br />
It should be emphasised that <strong>the</strong>se uncerta<strong>in</strong> results do not mean that light <strong>in</strong>tensity has no<br />
effect on rate of pho<strong>to</strong>syn<strong>the</strong>sis, but simply that <strong>the</strong> experiment is <strong>in</strong>conclusive. This is a good<br />
exercise <strong>to</strong> see if pupils can look at data <strong>in</strong> an impartial way. They are likely <strong>to</strong> know that<br />
<strong>in</strong>creas<strong>in</strong>g light <strong>in</strong>tensity should <strong>in</strong>crease rate of pho<strong>to</strong>syn<strong>the</strong>sis, <strong>and</strong> this may lead <strong>the</strong>m <strong>to</strong><br />
exhibit bias when <strong>in</strong>terpret<strong>in</strong>g <strong>the</strong> results.<br />
_ Why study respiration (pages 40–41)____________<br />
PRACTICAL How can we measure respiration<br />
(pages 40–41)<br />
1. Expla<strong>in</strong> your results for flask A.<br />
The seeds will be respir<strong>in</strong>g, <strong>and</strong> respiration produces heat, which is reta<strong>in</strong>ed by <strong>the</strong> flask.<br />
2. Expla<strong>in</strong> <strong>the</strong> purpose of flask B.<br />
Flask B is a control <strong>to</strong> show that <strong>the</strong> effect is due <strong>to</strong> a liv<strong>in</strong>g process (respiration) <strong>in</strong> <strong>the</strong><br />
seeds.<br />
10
WJEC GCSE Additional Science Teacher’s Notes<br />
3. Why were <strong>the</strong> seeds <strong>in</strong> flask B r<strong>in</strong>sed <strong>in</strong> dis<strong>in</strong>fectant (Th<strong>in</strong>k what is likely <strong>to</strong> happen <strong>to</strong> dead seeds.)<br />
To prevent bacteria grow<strong>in</strong>g on <strong>the</strong> seeds (because bacteria would respire).<br />
4. Why were <strong>the</strong> seeds <strong>in</strong> flask A not r<strong>in</strong>sed <strong>in</strong> dis<strong>in</strong>fectant<br />
Liv<strong>in</strong>g seeds will not have very large numbers of bacteria grow<strong>in</strong>g on <strong>the</strong>m; <strong>the</strong>re would be<br />
a possibility of <strong>the</strong> dis<strong>in</strong>fectant damag<strong>in</strong>g <strong>the</strong> seeds.<br />
5. Although <strong>the</strong>re were roughly <strong>the</strong> same number of seeds <strong>in</strong> flask A <strong>and</strong> flask B, it is not necessary <strong>to</strong><br />
have <strong>the</strong> same number (or <strong>the</strong> same mass) of beans <strong>in</strong> each flask. Why not<br />
We are only compar<strong>in</strong>g whe<strong>the</strong>r heat is generated or not, we are not compar<strong>in</strong>g <strong>the</strong> amount<br />
of heat generated. The number of seeds should be more or less <strong>the</strong> same, however.<br />
6. Suggest a reason why it would not be a good idea <strong>to</strong> leave <strong>the</strong> seeds for much more than 24 hours<br />
before tak<strong>in</strong>g <strong>the</strong> second read<strong>in</strong>g.<br />
If <strong>the</strong> seeds germ<strong>in</strong>ate, <strong>the</strong> new plants would have no access <strong>to</strong> light <strong>and</strong> may die.<br />
_How do organisms survive <strong>in</strong> places with very little___<br />
oxygen (pages 42–44)<br />
PRACTICAL How can we measure anaerobic respiration<br />
<strong>in</strong> yeast (page 43)<br />
1. Count<strong>in</strong>g bubbles per m<strong>in</strong>ute is not a very accurate way <strong>to</strong> measure carbon dioxide production (<strong>and</strong><br />
<strong>the</strong>refore respiration). Why not<br />
The bubbles may be difficult <strong>to</strong> count if <strong>the</strong>y emerge quickly <strong>and</strong> <strong>in</strong> clusters, lead<strong>in</strong>g <strong>to</strong><br />
errors. The bubbles are not identical <strong>in</strong> size <strong>and</strong> so number of bubbles is not exactly<br />
equivalent <strong>to</strong> volume of gas.<br />
2. How could <strong>the</strong> accuracy be improved<br />
The easiest way would be <strong>to</strong> collect <strong>the</strong> gas over water or <strong>in</strong> a gas syr<strong>in</strong>ge <strong>and</strong> measure <strong>the</strong><br />
volume. Us<strong>in</strong>g glass tub<strong>in</strong>g with a wider bore would slow <strong>the</strong> emergence of <strong>the</strong> bubbles <strong>and</strong><br />
reduce experimental error slightly.<br />
3. From your results, do you th<strong>in</strong>k that five repeats were enough Expla<strong>in</strong> your answer.<br />
The answer will depend on <strong>the</strong> variation <strong>in</strong> <strong>the</strong> results.<br />
4. Design an experiment <strong>to</strong> test <strong>the</strong> effect of temperature on anaerobic respiration <strong>in</strong> yeast. Ensure that<br />
<strong>the</strong> experiment is fair, <strong>and</strong> as accurate <strong>and</strong> repeatable as possible. Include a risk assessment for<br />
your experiment.<br />
Features <strong>to</strong> look for:<br />
Control of temperature us<strong>in</strong>g water baths.<br />
Range of at least five temperatures, avoid<strong>in</strong>g very high temperatures which would<br />
certa<strong>in</strong>ly denature enzymes <strong>and</strong> kill <strong>the</strong> yeast (suggested – no higher than 60 °C).<br />
Control of:<br />
• concentration of glucose <strong>in</strong> <strong>the</strong> solution<br />
• ‘concentration’ of yeast <strong>in</strong> solution<br />
11
WJEC GCSE Additional Science Teacher’s Notes<br />
<br />
<br />
• volume of yeast <strong>and</strong> glucose solution<br />
• time period for read<strong>in</strong>g.<br />
Better pupils may suggest controll<strong>in</strong>g pH if <strong>the</strong>y have enough knowledge of enzymes.<br />
This would be relevant as carbon dioxide produced may lower pH.<br />
Risk assessment: <strong>the</strong> only hazard is <strong>the</strong> glass tub<strong>in</strong>g, which could break when <strong>the</strong> bung<br />
is <strong>in</strong>serted. Precaution – hold bung <strong>and</strong> not tub<strong>in</strong>g when <strong>in</strong>sert<strong>in</strong>g. Possibility of yeast<br />
allergy is irrelevant as <strong>the</strong> experiment does not <strong>in</strong>volve <strong>in</strong>gest<strong>in</strong>g <strong>the</strong> yeast.<br />
PRACTICAL What effects do respiration <strong>and</strong><br />
pho<strong>to</strong>syn<strong>the</strong>sis have on <strong>the</strong> atmosphere<br />
(pages 43–44)<br />
1. Expla<strong>in</strong> <strong>the</strong> f<strong>in</strong>al colour seen <strong>in</strong> each tube.<br />
Tube A: Little or no change <strong>in</strong> colour, because <strong>the</strong> carbon dioxide produced by respiration<br />
<strong>in</strong> <strong>the</strong> snails is absorbed by pho<strong>to</strong>syn<strong>the</strong>sis <strong>in</strong> <strong>the</strong> pond weed.<br />
Tube B: Goes red because carbon dioxide is be<strong>in</strong>g absorbed by <strong>the</strong> pond weed dur<strong>in</strong>g<br />
pho<strong>to</strong>syn<strong>the</strong>sis.<br />
Tube C: Goes yellow because <strong>the</strong> pond weed is respir<strong>in</strong>g (produc<strong>in</strong>g carbon dioxide) but<br />
cannot pho<strong>to</strong>syn<strong>the</strong>sise because of <strong>the</strong> lack of light.<br />
Tube D: Goes yellow because <strong>the</strong> snails are respir<strong>in</strong>g (produc<strong>in</strong>g carbon dioxide).<br />
Tube E: No change because noth<strong>in</strong>g <strong>in</strong> it will ei<strong>the</strong>r use or produce carbon dioxide – it’s a<br />
control.<br />
Note that <strong>the</strong> balance between respiration <strong>and</strong> pho<strong>to</strong>syn<strong>the</strong>sis <strong>in</strong> tube A is not likely <strong>to</strong> be<br />
perfect, so <strong>the</strong>re may be a slight change <strong>in</strong> colour.<br />
2. What was <strong>the</strong> purpose of:<br />
a tube C<br />
To show that pho<strong>to</strong>syn<strong>the</strong>sis was responsible for colour change <strong>in</strong> tube B (<strong>and</strong> <strong>the</strong>refore,<br />
by implication, <strong>in</strong> tube A)<br />
b tube E<br />
Control tube <strong>to</strong> show no colour change occurs without snails <strong>and</strong> pond weed. Also<br />
useful as a colour comparison for tube A.<br />
3. Why were <strong>the</strong> tubes sealed with cot<strong>to</strong>n wool ra<strong>the</strong>r than a cork or bung<br />
To allow gases <strong>in</strong> for pho<strong>to</strong>syn<strong>the</strong>sis <strong>and</strong>/or respiration (particularly <strong>in</strong> tubes B–D). Will<br />
also avoid build-up of pressure <strong>in</strong> tubes B–D (though this is unlikely <strong>to</strong> be a problem).<br />
Questions<br />
1. Expla<strong>in</strong> <strong>the</strong> trends shown <strong>in</strong> <strong>the</strong> graph (Figure 4.13).<br />
Between dawn <strong>and</strong> dusk, carbon dioxide levels decrease <strong>and</strong> oxygen levels <strong>in</strong>crease due <strong>to</strong><br />
pho<strong>to</strong>syn<strong>the</strong>sis exceed<strong>in</strong>g respiration. Between dusk <strong>and</strong> dawn <strong>the</strong> reverse happens because<br />
pho<strong>to</strong>syn<strong>the</strong>sis does not occur due <strong>to</strong> lack of light, but respiration cont<strong>in</strong>ues. Look for an<br />
underst<strong>and</strong><strong>in</strong>g that both pho<strong>to</strong>syn<strong>the</strong>sis <strong>and</strong> respiration occur <strong>in</strong> <strong>the</strong> dawn <strong>to</strong> dusk<br />
period.<br />
12
WJEC GCSE Additional Science Teacher’s Notes<br />
2. The greenhouse conta<strong>in</strong>s very few animals. What changes would you expect <strong>to</strong> see <strong>in</strong> this graph if<br />
<strong>the</strong>re was a mixed population of animals <strong>and</strong> plants<br />
In <strong>the</strong> dawn <strong>to</strong> dusk period, <strong>the</strong>re would be less change <strong>in</strong> <strong>the</strong> levels of both carbon dioxide <strong>and</strong><br />
oxygen. In <strong>the</strong> dusk <strong>to</strong> dawn period, <strong>the</strong> fall <strong>in</strong> oxygen <strong>and</strong> rise <strong>in</strong> carbon dioxide would both<br />
<strong>in</strong>crease.<br />
13
WJEC GCSE Additional Science Teacher’s Notes<br />
5<br />
The respira<strong>to</strong>ry system<br />
_How do we brea<strong>the</strong> (pages 47–48)_______________<br />
Questions<br />
1. Expla<strong>in</strong> why <strong>the</strong> balloons <strong>in</strong>flate when <strong>the</strong> sheet is pulled down, <strong>and</strong> deflate when it is pushed up.<br />
The balloons <strong>in</strong>flate when <strong>the</strong> sheet is pulled down because that creates more volume/space<br />
around <strong>the</strong> balloons which results <strong>in</strong> a lower pressure. The (now) higher pressure <strong>in</strong>side <strong>the</strong><br />
balloons forces <strong>the</strong>m outwards, caus<strong>in</strong>g <strong>in</strong>flation. When <strong>the</strong> sheet is raised, <strong>the</strong> process is<br />
reversed, result<strong>in</strong>g <strong>in</strong> a higher pressure outside <strong>the</strong> balloons than <strong>in</strong>side.<br />
2. List <strong>the</strong> ways <strong>in</strong> which this model of <strong>the</strong> respira<strong>to</strong>ry system is <strong>in</strong>accurate.<br />
The lungs are not like balloons – <strong>the</strong>y are more like sponges.<br />
The ‘ribcage’ on <strong>the</strong> model does not move.<br />
There is more space around <strong>the</strong> balloons than around <strong>the</strong> lungs.<br />
3. Do <strong>the</strong>se <strong>in</strong>accuracies mean that it is not a useful model of <strong>the</strong> respira<strong>to</strong>ry mechanism Expla<strong>in</strong> your<br />
answer.<br />
It is still a useful model because it illustrates how diaphragm movement affects pressure <strong>and</strong><br />
<strong>the</strong>n how this alters <strong>the</strong> shape of <strong>the</strong> lungs. It is a qualitative model <strong>and</strong> <strong>the</strong> <strong>in</strong>accuracies would<br />
only affect <strong>the</strong> scale of <strong>the</strong> effect.<br />
_How does <strong>the</strong> air we brea<strong>the</strong> <strong>in</strong> differ from that we___<br />
brea<strong>the</strong> out (pages 49–50)<br />
Questions<br />
4. Why is <strong>the</strong> exhaled air warmer than <strong>the</strong> <strong>in</strong>haled air<br />
The body is warmer than <strong>the</strong> environment <strong>and</strong> so it warms <strong>the</strong> air.<br />
5. Why does exhaled air have more water vapour<br />
The l<strong>in</strong><strong>in</strong>g of <strong>the</strong> alveoli is damp which moistens <strong>the</strong> air.<br />
6. Expla<strong>in</strong> <strong>the</strong> change <strong>in</strong> <strong>the</strong> percentage of nitrogen <strong>in</strong> exhaled air (note: <strong>the</strong> body nei<strong>the</strong>r absorbs nor<br />
gives out nitrogen).<br />
The reduction of oxygen <strong>and</strong> <strong>the</strong> <strong>in</strong>crease <strong>in</strong> carbon dioxide roughly balance each o<strong>the</strong>r. Water<br />
vapour is added which <strong>in</strong>creases <strong>the</strong> overall volume. Therefore <strong>the</strong> percentage of <strong>the</strong> air that is<br />
nitrogen goes down, even though <strong>the</strong> actual amount of nitrogen stays <strong>the</strong> same. (There would<br />
also be a slight decrease <strong>in</strong> <strong>the</strong> percentage of o<strong>the</strong>r gases, but as <strong>the</strong> number is so small, <strong>the</strong><br />
change is masked when figures are rounded.)<br />
Though dem<strong>and</strong><strong>in</strong>g, this question is a good test of whe<strong>the</strong>r pupils have a full underst<strong>and</strong><strong>in</strong>g<br />
of percentages.<br />
14
WJEC GCSE Additional Science Teacher’s Notes<br />
PRACTICAL Demonstrat<strong>in</strong>g <strong>the</strong> difference <strong>in</strong> carbon<br />
dioxide content of <strong>in</strong>haled <strong>and</strong> exhaled air<br />
(page 50)<br />
1. What are your conclusions from this experiment<br />
There is more carbon dioxide <strong>in</strong> exhaled air than <strong>in</strong> <strong>in</strong>haled air.<br />
2. A student put forward a hypo<strong>the</strong>sis that ‘There is carbon dioxide <strong>in</strong> exhaled air but not <strong>in</strong> <strong>in</strong>haled air’.<br />
a Expla<strong>in</strong> why <strong>the</strong> evidence from this experiment cannot support this hypo<strong>the</strong>sis.<br />
The test is not sensitive <strong>to</strong> small amounts of carbon dioxide, so <strong>the</strong> fact that <strong>the</strong> ‘<strong>in</strong>haled<br />
air’ lime water stays clear does not conclusively prove that <strong>the</strong>re is no carbon dioxide <strong>in</strong><br />
<strong>in</strong>haled air.<br />
b<br />
Suggest how you could modify <strong>the</strong> procedure <strong>to</strong> test this hypo<strong>the</strong>sis.<br />
The lime water should be switched for bicarbonate <strong>in</strong>dica<strong>to</strong>r (pupils may just say ‘a<br />
more sensitive <strong>in</strong>dica<strong>to</strong>r’).<br />
Discussion po<strong>in</strong>t<br />
Why does <strong>in</strong>haled air come <strong>in</strong> through tube A <strong>and</strong> exhaled air go out through tube B<br />
The tube attached <strong>to</strong> <strong>the</strong> mouth <strong>in</strong> A has its end <strong>in</strong> air, whereas <strong>in</strong> B it’s <strong>in</strong> water. There is<br />
<strong>the</strong>refore less resistance <strong>to</strong> air flow <strong>in</strong> A, so air comes <strong>in</strong> from tube A. When air is brea<strong>the</strong>d<br />
back <strong>in</strong><strong>to</strong> <strong>the</strong> tubes, it is actually equally easy for <strong>the</strong> air <strong>to</strong> travel down ei<strong>the</strong>r tube, <strong>and</strong> <strong>in</strong>deed<br />
some will go back <strong>in</strong><strong>to</strong> tube A. However, <strong>the</strong> effect is more noticeable <strong>in</strong> B because <strong>the</strong> air goes<br />
directly <strong>in</strong><strong>to</strong> <strong>the</strong> lime water.<br />
_How does smok<strong>in</strong>g damage <strong>the</strong> lungs (pages 51–53)_<br />
Questions<br />
7. Compare <strong>the</strong> data of a lifelong non-smoker with someone giv<strong>in</strong>g up at 30. Roughly how much more<br />
likely is <strong>the</strong> smoker <strong>to</strong> develop lung cancer before <strong>the</strong> age of 65<br />
About 1% more likely.<br />
8. Suggest a reason why, if you smoke, it is best <strong>to</strong> give up before <strong>the</strong> age of 40.<br />
Giv<strong>in</strong>g up later than 40 produces less decrease <strong>in</strong> risk than giv<strong>in</strong>g up at 40 or earlier.<br />
Discussion po<strong>in</strong>ts<br />
Overall, smokers are about 15 times more likely <strong>to</strong> get lung cancer than non-smokers. In itself, however,<br />
this does not prove that smok<strong>in</strong>g causes lung cancer. Why not, <strong>and</strong> what extra evidence is needed <strong>to</strong> show<br />
a causal l<strong>in</strong>k<br />
The po<strong>in</strong>t <strong>to</strong> stress here is that correlation does not prove a causal relationship. The extra evidence<br />
is a mechanism l<strong>in</strong>k<strong>in</strong>g smok<strong>in</strong>g <strong>and</strong> cancer, which has been found. The carc<strong>in</strong>ogens <strong>in</strong> cigarette<br />
smoke provide clear evidence that smok<strong>in</strong>g is likely <strong>to</strong> cause cancer.<br />
15
WJEC GCSE Additional Science Teacher’s Notes<br />
PRACTICAL What’s <strong>in</strong> cigarette smoke (page 53)<br />
1. Suggest a reason for <strong>the</strong> colour change <strong>in</strong> <strong>the</strong> <strong>in</strong>dica<strong>to</strong>r.<br />
Carbon monoxide <strong>and</strong> carbon dioxide produced by <strong>the</strong> burn<strong>in</strong>g of <strong>to</strong>bacco are acid gases.<br />
2. Good practice <strong>in</strong> this experiment is <strong>to</strong> first suck air through an unlit cigarette for 10 m<strong>in</strong>utes. Suggest<br />
a reason for this.<br />
To ensure that changes are due <strong>to</strong> <strong>to</strong>bacco smoke <strong>and</strong> not atmospheric air (pass<strong>in</strong>g through<br />
<strong>the</strong> <strong>to</strong>bacco).<br />
3. The colour <strong>and</strong> smell of <strong>the</strong> cot<strong>to</strong>n wool shows <strong>the</strong> presence of tar. It is difficult <strong>to</strong> measure colour or<br />
smell. Suggest how <strong>the</strong> procedure could be adjusted so that <strong>the</strong> amount of tar <strong>in</strong> two different types<br />
of cigarettes could be compared.<br />
The cot<strong>to</strong>n wool could be weighed before <strong>and</strong> after <strong>the</strong> experiment.<br />
_How have attitudes <strong>to</strong> smok<strong>in</strong>g changed __________<br />
(pages 53–54)<br />
TASK What are <strong>the</strong> dangers of passive smok<strong>in</strong>g<br />
(page 54)<br />
In <strong>the</strong> report <strong>to</strong> be written for this section, pupils are asked <strong>to</strong> consider bias. A common<br />
misunderst<strong>and</strong><strong>in</strong>g is that anyth<strong>in</strong>g reported by a biased website is untrue. Pupils should<br />
underst<strong>and</strong> that bias is often evident <strong>in</strong> <strong>the</strong> selection of <strong>in</strong>formation reported <strong>and</strong> ‘skewed’<br />
<strong>in</strong>terpretation of data. Sometimes, however, biased groups can present reliable <strong>in</strong>formation.<br />
This is usually when <strong>the</strong>ir particular bias aligns with <strong>the</strong> scientific evidence.<br />
16
WJEC GCSE Additional Science Teacher’s Notes<br />
6<br />
Digestion<br />
_Why do we digest food (pages 56–57)____________<br />
PRACTICAL Us<strong>in</strong>g a ‘model gut’ (pages 56–57)<br />
1. Expla<strong>in</strong> what your results show about <strong>the</strong> gut <strong>and</strong> digestion.<br />
The results show that starch cannot pass out of <strong>the</strong> gut <strong>in</strong><strong>to</strong> <strong>the</strong> blood, but glucose can.<br />
Therefore, starch has <strong>to</strong> be digested <strong>in</strong><strong>to</strong> glucose <strong>in</strong> order for it <strong>to</strong> be used by <strong>the</strong> body.<br />
2. Suggest why it is better <strong>to</strong> use a boil<strong>in</strong>g tube <strong>in</strong> this experiment, ra<strong>the</strong>r than a beaker, which would<br />
hold more water.<br />
The quantity of glucose go<strong>in</strong>g <strong>in</strong><strong>to</strong> <strong>the</strong> water from <strong>the</strong> visk<strong>in</strong>g tub<strong>in</strong>g is likely <strong>to</strong> be small.<br />
The more water <strong>the</strong>re is, <strong>the</strong> more dilute <strong>the</strong> glucose solution will be, <strong>and</strong> if it is <strong>to</strong>o dilute,<br />
<strong>the</strong> cl<strong>in</strong>istix will not detect it.<br />
Discussion po<strong>in</strong>t<br />
How good a model of <strong>the</strong> gut <strong>and</strong> blood system do you th<strong>in</strong>k this apparatus is Justify your op<strong>in</strong>ion.<br />
The visk<strong>in</strong>g tub<strong>in</strong>g has similar properties <strong>to</strong> <strong>the</strong> l<strong>in</strong><strong>in</strong>g of <strong>the</strong> gut <strong>and</strong> so from that po<strong>in</strong>t of view<br />
<strong>the</strong> model is good. Blood is mostly water so us<strong>in</strong>g water as a model for blood is reasonable.<br />
However, <strong>the</strong>re are o<strong>the</strong>r tissues <strong>in</strong> <strong>the</strong> gut between <strong>the</strong> l<strong>in</strong><strong>in</strong>g <strong>and</strong> <strong>the</strong> blood vessels, <strong>and</strong> o<strong>the</strong>r<br />
substances <strong>in</strong> <strong>the</strong> gut <strong>and</strong> <strong>the</strong> blood which may affect <strong>the</strong> process, so <strong>the</strong> model has some<br />
weaknesses. As <strong>the</strong> experiment is qualitative ra<strong>the</strong>r than quantitative, <strong>the</strong> model is adequate.<br />
_What food needs digest<strong>in</strong>g (pages 57–58)_________<br />
Question<br />
1. When people need energy very rapidly (e.g. athletes before strenuous exercise, diabetics with low<br />
blood sugar levels) <strong>the</strong>y take glucose tablets or dr<strong>in</strong>ks. Why would glucose be a particularly good<br />
source of rapid energy<br />
Glucose is high <strong>in</strong> energy <strong>and</strong> is already a simple sugar which can pass through <strong>the</strong> gut wall<br />
without be<strong>in</strong>g digested. It would <strong>the</strong>refore get <strong>in</strong><strong>to</strong> <strong>the</strong> blood quicker than most o<strong>the</strong>r<br />
carbohydrates.<br />
PRACTICAL How do we know what our food conta<strong>in</strong>s<br />
(page 58)<br />
1. The more sugar <strong>the</strong>re is <strong>in</strong> <strong>the</strong> solution, <strong>the</strong> fur<strong>the</strong>r <strong>the</strong> colour change <strong>in</strong> <strong>the</strong> Benedict’s solution<br />
goes. This gives an <strong>in</strong>dication, but not a measure, of how much glucose is <strong>in</strong> <strong>the</strong> solution. Suggest<br />
how you might get an actual measure of <strong>the</strong> amount of glucose <strong>in</strong> a solution, us<strong>in</strong>g <strong>the</strong> Benedict’s<br />
test.<br />
If you did <strong>the</strong> test with a series of different concentrations of glucose, <strong>and</strong> ran it for a set<br />
17
WJEC GCSE Additional Science Teacher’s Notes<br />
time, you could produce a colour chart <strong>to</strong> show how colour matched <strong>the</strong> concentration.<br />
2. How accurate do you th<strong>in</strong>k your measure (from question 1) would be Give reasons for your<br />
answer.<br />
Not very accurate. There would be more possible concentrations of glucose solution than<br />
<strong>the</strong>re would be colour changes, <strong>and</strong> once <strong>the</strong> colour had gone <strong>to</strong> brick red any fur<strong>the</strong>r<br />
<strong>in</strong>crease <strong>in</strong> concentration would not be detectable.<br />
_ Where <strong>in</strong> <strong>the</strong> body is food digested (pages 59–60)__<br />
Question<br />
2. As well as digest<strong>in</strong>g prote<strong>in</strong>s, <strong>the</strong> s<strong>to</strong>mach also conta<strong>in</strong>s acid, which kills off bacteria present <strong>in</strong> <strong>the</strong><br />
food. Why do you th<strong>in</strong>k this acid is best placed <strong>in</strong> <strong>the</strong> s<strong>to</strong>mach ra<strong>the</strong>r than <strong>in</strong><br />
a <strong>the</strong> small <strong>in</strong>test<strong>in</strong>e<br />
It is better <strong>to</strong> kill <strong>the</strong> bacteria as soon as possible. The food enters <strong>the</strong> s<strong>to</strong>mach before it<br />
enters <strong>the</strong> small <strong>in</strong>test<strong>in</strong>e.<br />
b <strong>the</strong> mouth<br />
Various <strong>answers</strong> are possible:<br />
The food does not stay <strong>in</strong> <strong>the</strong> mouth for very long.<br />
The acid would affect <strong>the</strong> taste of food.<br />
The acid could rot <strong>the</strong> teeth.<br />
_What does bile do (pages 61–62)________________<br />
PRACTICAL What are <strong>the</strong> optimum conditions for lipase<br />
enzymes (pages 61–62)<br />
1. What effect did temperature have on <strong>the</strong> enzyme activity<br />
Activity should <strong>in</strong>crease as temperature rises, until <strong>the</strong> po<strong>in</strong>t of denaturation. Denaturation<br />
may not be observed, however.<br />
2. What effect did <strong>the</strong> liquid detergent have on enzyme activity<br />
The detergent should <strong>in</strong>crease <strong>the</strong> enzyme activity (but pupils must <strong>in</strong>terpret <strong>the</strong> data <strong>the</strong>y<br />
obta<strong>in</strong>, whatever it shows).<br />
3. Look<strong>in</strong>g at <strong>the</strong> results, do you th<strong>in</strong>k <strong>the</strong>y were accurate Give a reason for your answer.<br />
The judgement here will depend on <strong>the</strong> data obta<strong>in</strong>ed.<br />
4. Suggest one possible source of <strong>in</strong>accuracy <strong>in</strong> this experiment.<br />
The ma<strong>in</strong> source of <strong>in</strong>accuracy is <strong>the</strong> difficulty <strong>in</strong> judg<strong>in</strong>g <strong>the</strong> exact po<strong>in</strong>t at which <strong>the</strong><br />
<strong>in</strong>dica<strong>to</strong>r changes from p<strong>in</strong>k <strong>to</strong> colourless. There may be some temperature fluctuation <strong>in</strong> <strong>the</strong><br />
non-electronic water baths.<br />
18
WJEC GCSE Additional Science Teacher’s Notes<br />
7<br />
Biodiversity <strong>and</strong> <strong>the</strong><br />
environment<br />
_How can biodiversity be ma<strong>in</strong>ta<strong>in</strong>ed (pages 65–66)__<br />
Questions<br />
1. Suggest a possible reason for <strong>the</strong> decl<strong>in</strong>e <strong>in</strong> woodl<strong>and</strong> birds s<strong>in</strong>ce 1970.<br />
Loss of habitat (tree fell<strong>in</strong>g)<br />
Decrease <strong>in</strong> prey populations<br />
Increase <strong>in</strong> preda<strong>to</strong>r populations<br />
Disease<br />
Loss of habitat is a more likely explanation than <strong>the</strong> o<strong>the</strong>rs.<br />
2. Suggest a possible reason for <strong>the</strong> decl<strong>in</strong>e <strong>in</strong> farml<strong>and</strong> birds s<strong>in</strong>ce 1970.<br />
As for Question 1. However, habitat loss is a less likely cause (though <strong>the</strong>re has been some loss<br />
on farml<strong>and</strong>), <strong>and</strong> decl<strong>in</strong>e <strong>in</strong> prey populations is a more likely cause, as much of <strong>the</strong>ir prey<br />
would be <strong>in</strong>sect pests which have been reduced by farml<strong>and</strong> management.<br />
3. The graphs go up <strong>to</strong> 2008. What do you th<strong>in</strong>k would happen <strong>to</strong> <strong>the</strong> populations of <strong>the</strong> different types of<br />
bird if fur<strong>the</strong>r data had been published for 2010 Expla<strong>in</strong> your answer.<br />
Seabirds <strong>and</strong> water <strong>and</strong> wetl<strong>and</strong> bird populations look roughly stable. Woodl<strong>and</strong> birds have an<br />
upturn <strong>in</strong> 2008 which might cont<strong>in</strong>ue. Farml<strong>and</strong> birds seem <strong>to</strong> be <strong>in</strong> slow decl<strong>in</strong>e but <strong>the</strong> 2008<br />
figure suggests this may be levell<strong>in</strong>g off.<br />
Note that for all three <strong>questions</strong>, def<strong>in</strong>ite <strong>answers</strong> cannot be given. Teachers should assess on <strong>the</strong><br />
basis of communication skills <strong>and</strong> <strong>the</strong> thought given <strong>to</strong> <strong>the</strong> <strong>answers</strong>. Answers should be reasonable,<br />
<strong>and</strong> would be better if justified (Question 3 requires justification).<br />
Discussion po<strong>in</strong>t<br />
Suggest how <strong>the</strong> data <strong>in</strong> <strong>the</strong> graph might help <strong>to</strong> f<strong>in</strong>d reasons for <strong>the</strong> decl<strong>in</strong>e <strong>in</strong> woodl<strong>and</strong> <strong>and</strong> farml<strong>and</strong><br />
birds.<br />
There is no direct evidence <strong>in</strong> <strong>the</strong> graph for reasons for <strong>the</strong> decl<strong>in</strong>e. However, <strong>the</strong> graph does<br />
provide some useful clues:<br />
Significant decl<strong>in</strong>e <strong>in</strong> farml<strong>and</strong> birds started around 1980 <strong>and</strong> woodl<strong>and</strong> birds around 1990. It<br />
would be useful <strong>to</strong> look for any changes that <strong>to</strong>ok place <strong>in</strong> those habitats at those times.<br />
The clear divergence <strong>in</strong> <strong>the</strong> different populations <strong>in</strong>dicates that <strong>the</strong> cause is l<strong>in</strong>ked <strong>to</strong> <strong>the</strong><br />
habitat, it is not just someth<strong>in</strong>g happen<strong>in</strong>g <strong>to</strong> birds <strong>in</strong> general.<br />
_How can we get data about biodiversity <strong>in</strong> an_______<br />
environment (pages 67–68)<br />
Questions<br />
4. Scientists sampled an area of 1000 m 2 on a beach that had an area of 1 km 2 (1 000 000 m 2 ). They<br />
found 293 cockles. Estimate how many cockles <strong>the</strong>re were on <strong>the</strong> whole beach.<br />
19
WJEC GCSE Additional Science Teacher’s Notes<br />
The sampled area represents 1000/1 000 000 (1/1000) of <strong>the</strong> whole beach. Therefore, <strong>the</strong><br />
number of cockles on <strong>the</strong> whole beach will be 293 x 1000 = 293 000<br />
5. Look at <strong>the</strong> environments <strong>in</strong> Figure 7.5. Suggest a reason why scientists would need <strong>to</strong> use a bigger<br />
sample area <strong>in</strong> woodl<strong>and</strong> than <strong>in</strong> <strong>the</strong> saltmarsh.<br />
The saltmarsh is a much more homogenous habitat. A sample taken from anywhere is likely <strong>to</strong><br />
be similar <strong>to</strong> any o<strong>the</strong>r area. In <strong>the</strong> woodl<strong>and</strong> <strong>the</strong>re is much more diversity with<strong>in</strong> <strong>the</strong> habitat<br />
<strong>and</strong> samples from (e.g.) open areas may be significantly different from those <strong>in</strong> <strong>the</strong> midst of<br />
tree cover.<br />
PRACTICAL Count<strong>in</strong>g daisies (page 68)<br />
Suggest any possible disadvantages of <strong>the</strong> method used <strong>to</strong> place <strong>the</strong> quadrat r<strong>and</strong>omly.<br />
It is not really r<strong>and</strong>om. It is perfectly possible <strong>to</strong> look beh<strong>in</strong>d you <strong>and</strong> <strong>the</strong>re is a choice of place<br />
<strong>to</strong> st<strong>and</strong>. A better method would be <strong>to</strong> divide <strong>the</strong> area <strong>in</strong><strong>to</strong> a marked grid of squares, with each<br />
square <strong>the</strong> size of <strong>the</strong> quadrat used. Allocate each square a number <strong>and</strong> use a r<strong>and</strong>om number<br />
genera<strong>to</strong>r <strong>to</strong> decide which squares <strong>to</strong> sample. Throw<strong>in</strong>g over <strong>the</strong> shoulder is less scientifically<br />
r<strong>and</strong>om but much quicker <strong>and</strong> easier <strong>to</strong> do.<br />
_How can we f<strong>in</strong>d out about <strong>the</strong> distribution of_______<br />
organisms (pages 68–70)<br />
PRACTICAL What effect does trampl<strong>in</strong>g have on plants<br />
(page 70)<br />
For Questions 1, 2 <strong>and</strong> 4 <strong>the</strong> <strong>answers</strong> will depend upon results obta<strong>in</strong>ed.<br />
For Question 3 <strong>the</strong> answer will depend upon <strong>the</strong> site chosen, but light <strong>in</strong>tensity is a likely fac<strong>to</strong>r.<br />
_How can we measure an animal population that moves<br />
around (pages 71–72)<br />
Question<br />
6. Dave wanted <strong>to</strong> estimate <strong>the</strong> population of woodlice <strong>in</strong> his garden. He searched around <strong>and</strong> collected<br />
100 woodlice. He marked each of <strong>the</strong>m with a spot of white pa<strong>in</strong>t on its back, <strong>and</strong> released <strong>the</strong>m (see<br />
Figure 7.10). A week later he went <strong>in</strong><strong>to</strong> his garden <strong>and</strong> collected ano<strong>the</strong>r 100 woodlice. Four of those<br />
were marked ones that he had captured before. Us<strong>in</strong>g <strong>the</strong> equation given earlier <strong>in</strong> this section,<br />
calculate <strong>the</strong> size of <strong>the</strong> woodlouse population <strong>in</strong> Dave’s garden.<br />
100 100<br />
10000<br />
N 2500 woodlice<br />
4 4<br />
Discussion po<strong>in</strong>t<br />
How good do you th<strong>in</strong>k Dave’s experimental method was Could he have improved it <strong>in</strong> any way<br />
<br />
White pa<strong>in</strong>t is quite bright <strong>and</strong> could make <strong>the</strong> marked woodlice more noticeable <strong>to</strong> preda<strong>to</strong>rs,<br />
<strong>and</strong> more likely <strong>to</strong> be found when he <strong>to</strong>ok his second sample. A darker colour would have been<br />
better.<br />
20
WJEC GCSE Additional Science Teacher’s Notes<br />
He could have left <strong>the</strong>m for longer than a week or taken larger samples, but one week <strong>and</strong> a<br />
sample of 100 are reasonable.<br />
Overall <strong>the</strong> method is adequate, <strong>the</strong> only weakness be<strong>in</strong>g <strong>the</strong> colour of <strong>the</strong> pa<strong>in</strong>t.<br />
_Why can <strong>in</strong>troduc<strong>in</strong>g new species <strong>to</strong> an area cause<br />
problems (pages 72–74)<br />
TASK What are <strong>the</strong> advantages <strong>and</strong> disadvantage of<br />
biological control (page 74)<br />
On <strong>the</strong> <strong>in</strong>ternet, research <strong>the</strong> pros <strong>and</strong> cons of biological control, <strong>and</strong> some of <strong>the</strong> different methods<br />
used. Write a report on your f<strong>in</strong>d<strong>in</strong>gs.<br />
The criteria used for <strong>the</strong> controlled assessment research task could be applied here. In<br />
Additional Science, research <strong>and</strong> communication skills are assessed <strong>in</strong> a less specific way<br />
throughout <strong>the</strong> controlled assessment.<br />
21
WJEC GCSE Additional Science Teacher’s Notes<br />
8<br />
A<strong>to</strong>mic structure <strong>and</strong> <strong>the</strong><br />
Periodic Table<br />
_What is <strong>the</strong> structure of an a<strong>to</strong>m (pages 75–78)____<br />
Questions<br />
1. Look at <strong>the</strong> <strong>in</strong>formation about <strong>the</strong> sodium a<strong>to</strong>m. How many pro<strong>to</strong>ns, neutrons <strong>and</strong> electrons are <strong>the</strong>re <strong>in</strong><br />
<strong>the</strong> a<strong>to</strong>m<br />
11 pro<strong>to</strong>ns, 12 neutrons, 11 electrons.<br />
2. Us<strong>in</strong>g <strong>the</strong> <strong>in</strong>formation <strong>in</strong> Table 8.4, draw <strong>the</strong> a<strong>to</strong>ms of:<br />
a carbon b hydrogen<br />
2,4 1<br />
c silicon d potassium.<br />
2,8,4 2,8,8,1<br />
3. Which element’s a<strong>to</strong>m is shown <strong>in</strong> this diagram (Figure 8.4)<br />
Nitrogen<br />
4. Look at <strong>the</strong> first 20 elements, <strong>and</strong> which group <strong>the</strong>y are <strong>in</strong>. What is <strong>the</strong> connection between <strong>the</strong> group<br />
number <strong>and</strong> <strong>the</strong> electron configuration (Note: Hydrogen is not <strong>in</strong> a group.)<br />
The number of <strong>the</strong> group is <strong>the</strong> number of electrons <strong>in</strong> <strong>the</strong> outer shell of <strong>the</strong> element.<br />
5. For <strong>the</strong> first 20 elements, what is <strong>the</strong> relationship between <strong>the</strong> period <strong>the</strong> element is <strong>in</strong> <strong>and</strong> its electron<br />
configuration<br />
The period is <strong>the</strong> same as <strong>the</strong> number of electron shells <strong>in</strong> <strong>the</strong> a<strong>to</strong>m.<br />
22
WJEC GCSE Additional Science Teacher’s Notes<br />
_ How heavy is an a<strong>to</strong>m (pages 79–80)____________<br />
Questions<br />
6. F<strong>in</strong>d <strong>the</strong> relative molecular masses of:<br />
a ammonia, NH 3 14 + (3 x 1) = 17<br />
b methane, CH 4 12 + (4 x 1) = 16<br />
c hydrogen sulfide, H 2 S (2 x 1) + 32 = 34<br />
7. F<strong>in</strong>d <strong>the</strong> relative formula masses of:<br />
a calcium chloride, CaCl 2 40 + (2 x 35.5) = 111<br />
b copper(II) oxide, CuO 64 + 16 = 80<br />
23
WJEC GCSE Additional Science Teacher’s Notes<br />
9<br />
Alkali metals <strong>and</strong> halogens<br />
_The alkali metals (pages 83–91)__________________<br />
PRACTICAL Observ<strong>in</strong>g patterns of reactivity – <strong>the</strong> alkali<br />
metals (pages 87–89)<br />
Safety: take care with <strong>the</strong>se demonstrations <strong>and</strong> ensure that you consult <strong>the</strong> relevant CLEAPSS<br />
guidance.<br />
1. Which alkali metal reacts most vigorously with:<br />
a air Potassium<br />
b water Potassium<br />
c chlor<strong>in</strong>e Potassium<br />
2. Us<strong>in</strong>g your observations, arrange <strong>the</strong> three alkali metals <strong>in</strong> order of <strong>the</strong>ir reactivity (from least <strong>to</strong><br />
most reactive).<br />
Lithium <strong>the</strong>n sodium <strong>the</strong>n potassium<br />
3. Us<strong>in</strong>g a Periodic Table, arrange all <strong>the</strong> Group 1 metals <strong>in</strong> order of reactivity.<br />
Lithium, sodium, potassium, rubidium, caesium, francium<br />
4. How does reactivity vary as you move down Group 1 of <strong>the</strong> Periodic Table<br />
The elements get more reactive as you move down <strong>the</strong> Group.<br />
5. Look aga<strong>in</strong> at <strong>the</strong> electronic structure of <strong>the</strong> alkali metals <strong>in</strong> Table 9.1. Is <strong>the</strong>re a pattern between <strong>the</strong><br />
electron structure <strong>and</strong> <strong>the</strong> reactivity of <strong>the</strong> alkali metals Can you expla<strong>in</strong> this pattern<br />
Alkali metals all have a s<strong>in</strong>gle electron <strong>in</strong> <strong>the</strong>ir outer shell. The fur<strong>the</strong>r down <strong>the</strong> group, <strong>the</strong><br />
weaker this s<strong>in</strong>gle electron is held <strong>to</strong> <strong>the</strong> a<strong>to</strong>m (<strong>the</strong>re are more electron shells beneath it).<br />
The weaker <strong>the</strong> electron is held, <strong>the</strong> more reactive <strong>the</strong> metal.<br />
6. Predict <strong>the</strong> observations that you mighht make from <strong>the</strong> reactions of rubidium with oxygen (<strong>in</strong> air),<br />
water <strong>and</strong> chlor<strong>in</strong>e.<br />
Rubidium will react much more violently with all three reactants, explod<strong>in</strong>g on contact (see<br />
Discussion Po<strong>in</strong>t).<br />
7. Why are <strong>the</strong> reactions of potassium with chlor<strong>in</strong>e, <strong>and</strong> any of <strong>the</strong> o<strong>the</strong>r alkali metals with any of <strong>the</strong><br />
o<strong>the</strong>r chemicals, not allowed <strong>to</strong> be carried out <strong>in</strong> schools<br />
The reactions are far <strong>to</strong>o violent <strong>to</strong> be carried out us<strong>in</strong>g normal school facilities.<br />
8. Use <strong>the</strong> word <strong>and</strong> balanced symbol equations for lithium <strong>to</strong> produce similar word <strong>and</strong> balanced<br />
symbol equations for <strong>the</strong> reactions of sodium <strong>and</strong> potassium with oxygen, water <strong>and</strong> chlor<strong>in</strong>e.<br />
24
WJEC GCSE Additional Science Teacher’s Notes<br />
sodium + oxygen → sodium oxide<br />
4Na(s) + O 2 (g) → 2Na 2 O(s)<br />
sodium + water → sodium hydroxide + hydrogen<br />
2Na(s) + 2H 2 O(l) → 2NaOH(aq) + H 2 (g)<br />
sodium + chlor<strong>in</strong>e → sodium chloride<br />
2Na(s) + Cl 2 (g) → 2NaCl(s)<br />
potassium + oxygen → potassium oxide<br />
4K(s) + O 2 (g) → 2K 2 O(s)<br />
potassium + water → potassium hydroxide + hydrogen<br />
2K(s) + 2H 2 O(l) → 2KOH(aq) + H 2 (g)<br />
potassium + chlor<strong>in</strong>e → potassium chloride<br />
2K(s) + Cl 2 (g) → 2KCl(s)<br />
9. Brom<strong>in</strong>e is a halogen like chlor<strong>in</strong>e but it is less reactive than chlor<strong>in</strong>e gas. Predict <strong>the</strong> reactions of<br />
brom<strong>in</strong>e with lithium, sodium <strong>and</strong> potassium.<br />
Lithium burns readily <strong>in</strong> brom<strong>in</strong>e, as do sodium <strong>and</strong> potassium, <strong>the</strong> reactions becom<strong>in</strong>g<br />
more violent from sodium <strong>to</strong> potassium.<br />
10. Write word <strong>and</strong> balanced symbol equations for <strong>the</strong> reactions of brom<strong>in</strong>e with lithium, sodium <strong>and</strong><br />
potassium.<br />
lithium + brom<strong>in</strong>e → lithium bromide<br />
2Li(s) + Br 2 (g) → 2LiBr(s)<br />
sodium + brom<strong>in</strong>e → sodium bromide<br />
2Na(s) + Br 2 (g) → 2NaBr(s)<br />
potassium + brom<strong>in</strong>e → potassium bromide<br />
2K(s) + Br 2 (g) → 2KBr(s)<br />
Discussion po<strong>in</strong>t<br />
Rubidium <strong>and</strong> caesium react far <strong>to</strong>o violently with oxygen, water <strong>and</strong> chlor<strong>in</strong>e <strong>to</strong> be performed even by<br />
demonstration <strong>in</strong> schools. You can, however, see video clips onl<strong>in</strong>e of <strong>the</strong>se reactions occur<strong>in</strong>g under<br />
very special controlled conditions. The best example of this is Bra<strong>in</strong>iac: Science Abuse!<br />
www.youtube.com/watchv=eCkolYB_8co<br />
Show <strong>the</strong> YouTube clip <strong>in</strong> conjunction with Question 6 above.<br />
PRACTICAL Flame tests of alkali metal salts<br />
(pages 90–91)<br />
Safety – take care with <strong>the</strong>se practicals <strong>and</strong> ensure that you consult <strong>the</strong> relevant CLEAPSS<br />
guidance.<br />
1. Were <strong>the</strong>re any differences <strong>in</strong> <strong>the</strong> colours of <strong>the</strong> different alkali metal salts us<strong>in</strong>g <strong>the</strong> three different<br />
methods<br />
The flame colours will be very similar with each method.<br />
25
WJEC GCSE Additional Science Teacher’s Notes<br />
2. What were <strong>the</strong> patterns <strong>in</strong> <strong>the</strong> colours produced by:<br />
a lithium salts burn with a crimson (carm<strong>in</strong>e) red colour<br />
b sodium salts burn with an orangy-yellow colour<br />
c potassium salts potassium salts burn with a lilac colour<br />
3. Which method do you th<strong>in</strong>k produced <strong>the</strong> best results Expla<strong>in</strong> your answer.<br />
Student choice.<br />
4. Expla<strong>in</strong> how you could use this technique <strong>to</strong> identify any metal ion components of an unknown salt –<br />
for example, if a white powder was found at <strong>the</strong> scene of a crime, how could a flame test help <strong>to</strong><br />
identify <strong>the</strong> white powder<br />
S<strong>in</strong>ce many metal ions burn with characteristic ‘f<strong>in</strong>gerpr<strong>in</strong>t’ colours, <strong>the</strong> colour of <strong>the</strong> flame<br />
of <strong>the</strong> unknown white powder could identify <strong>the</strong> metal ion <strong>in</strong> <strong>the</strong> white powder.<br />
_Halogen reactions (pages 92–97)_________________<br />
PRACTICAL Observ<strong>in</strong>g <strong>the</strong> reaction of halogens with iron<br />
(pages 93–94)<br />
Safety – take care with <strong>the</strong>se practicals <strong>and</strong> ensure that you consult <strong>the</strong> relevant CLEAPSS<br />
guidance.<br />
1. Which halogen reacted most vigourously with <strong>the</strong> iron wool<br />
Chlor<strong>in</strong>e<br />
2. Arrange <strong>the</strong> three halogens <strong>in</strong> order of reactivity, from most reactive <strong>to</strong> least reactive.<br />
Chlor<strong>in</strong>e <strong>the</strong>n brom<strong>in</strong>e <strong>the</strong>n iod<strong>in</strong>e<br />
3. How does halogen reactivity vary as you go down Group 7<br />
Halogen reactivity decreases down <strong>the</strong> Group.<br />
4. Where would fluor<strong>in</strong>e <strong>and</strong> astat<strong>in</strong>e be on your halogen reactivity series<br />
Fluor<strong>in</strong>e would be above chlor<strong>in</strong>e <strong>and</strong> astat<strong>in</strong>e would be below iod<strong>in</strong>e.<br />
5. Write word <strong>and</strong> balanced symbol equations for <strong>the</strong> reactions of chlor<strong>in</strong>e, brom<strong>in</strong>e <strong>and</strong> iod<strong>in</strong>e with<br />
iron.<br />
iron + chlor<strong>in</strong>e → iron(III) chloride<br />
2Fe(s) + 3Cl 2 (g) → 2FeCl 3 (s)<br />
iron + brom<strong>in</strong>e → iron(III) bromide<br />
2Fe(s) + 3Br 2 (g) → 2FeBr 3 (s)<br />
iron + iod<strong>in</strong>e → iron(III) iodide<br />
2Fe(s) + 3I 2 (g) → 2FeI 3 (s)<br />
26
WJEC GCSE Additional Science Teacher’s Notes<br />
PRACTICAL Halogen displacement reactions<br />
(pages 94–95)<br />
Safety – take care with <strong>the</strong>se practicals <strong>and</strong> ensure that you consult <strong>the</strong> relevant CLEAPSS<br />
guidance.<br />
1. Will chlor<strong>in</strong>e displace brom<strong>in</strong>e from solutions of metal bromide <strong>and</strong> iod<strong>in</strong>e from metal iodies<br />
Yes<br />
2. Does reactivity <strong>in</strong>crease or decrease as you go up Group 7 of <strong>the</strong> Periodic Table How do <strong>the</strong><br />
results <strong>and</strong> observations of <strong>the</strong> halogen displacement reactions back this up<br />
Reactivity <strong>in</strong>creases up <strong>the</strong> group. Chlor<strong>in</strong>e displaces brom<strong>in</strong>e <strong>and</strong> iod<strong>in</strong>e; brom<strong>in</strong>e will<br />
only displace iod<strong>in</strong>e; iod<strong>in</strong>e will not displace ei<strong>the</strong>r.<br />
3. Write word <strong>and</strong> balanced symbol equations for <strong>the</strong> displacement of brom<strong>in</strong>e by chlor<strong>in</strong>e from<br />
solutions of:<br />
a<br />
b<br />
sodium bromide<br />
chlor<strong>in</strong>e + sodium bromide → brom<strong>in</strong>e + sodium chloride<br />
Cl 2 (g) + 2NaBr(aq) → Br 2 (l) + 2NaCl(aq)<br />
potassium bromide<br />
chlor<strong>in</strong>e + potassium bromide → brom<strong>in</strong>e + potassium chloride<br />
Cl 2 (g) + 2KBr(aq) → Br 2 (l) + 2KCl(aq)<br />
4. Write word <strong>and</strong> balanced symbol equations for <strong>the</strong> displacement of iod<strong>in</strong>e by chlor<strong>in</strong>e <strong>and</strong> <strong>the</strong>n by<br />
brom<strong>in</strong>e from solutions of:<br />
a<br />
b<br />
sodium iodide<br />
chlor<strong>in</strong>e + sodium iodide → iod<strong>in</strong>e + sodium chloride<br />
Cl 2 (g) + 2NaI(aq) → I 2 (l) + 2NaCl(aq)<br />
brom<strong>in</strong>e + sodium iodide → iod<strong>in</strong>e + sodium bromide<br />
Br 2 (g) + 2NaI(aq) → I 2 (l) + 2NaBr(aq)<br />
potassium iodide<br />
chlor<strong>in</strong>e + potassium iodide → iod<strong>in</strong>e + potassium chloride<br />
Cl 2 (g) + 2KI(aq) → I 2 (l) + 2KCl(aq)<br />
brom<strong>in</strong>e + potassium iodide → iod<strong>in</strong>e + potassium bromide<br />
Br 2 (g) + 2KI(aq) → I 2 (l) + 2KBr(aq)<br />
5. What would be <strong>the</strong> reaction between astat<strong>in</strong>e <strong>and</strong> sodium fluoride<br />
There would be no reaction.<br />
6. Describe <strong>the</strong> reaction between fluor<strong>in</strong>e with potassium iodide. What observations would you make<br />
Write word <strong>and</strong> balanced symbol equations for this reaction.<br />
A dark brown discoloration of iod<strong>in</strong>e would start <strong>to</strong> form as fluor<strong>in</strong>e gas was bubbled<br />
through potassium iodide.<br />
fluor<strong>in</strong>e + potassium iodide → iod<strong>in</strong>e + potassium fluoride<br />
F 2 (g) + 2KI(aq) → I 2 (l) + 2KF(aq)<br />
27
WJEC GCSE Additional Science Teacher’s Notes<br />
PRACTICAL The tests for halides (page 96)<br />
Safety – take care with <strong>the</strong>se practicals <strong>and</strong> ensure that you consult <strong>the</strong> relevant CLEAPSS<br />
guidance.<br />
Silver nitrate is quite expensive, encourage students <strong>to</strong> use spar<strong>in</strong>gly.<br />
1. What is <strong>the</strong> test for a chloride<br />
A white precipitate (that turns darker <strong>in</strong> sunlight) of silver chloride is formed when silver<br />
nitrate is added <strong>to</strong> a chloride salt.<br />
2. How are <strong>the</strong> tests for bromides <strong>and</strong> iodides different from chlorides<br />
Bromides produce pale yellow precipitates of silver bromide that are <strong>in</strong>soluble <strong>in</strong> dilute<br />
ammonia solution, but soluble <strong>in</strong> concentrated ammonia solution. Iodides produce yellow<br />
precipitates of silver iodide that are <strong>in</strong>soluble <strong>in</strong> ammonia solution.<br />
3. When is it important <strong>to</strong> add nitric acid <strong>to</strong> <strong>the</strong> test<br />
Nitric acid should be added when <strong>the</strong> test chemical is an unknown <strong>to</strong> prevent o<strong>the</strong>r ions such<br />
as carbonate <strong>and</strong> hydroxide <strong>in</strong>terfer<strong>in</strong>g with <strong>the</strong> silver nitrate reaction.<br />
4. Write balanced ionic symbol equations for <strong>the</strong> bromide test <strong>and</strong> <strong>the</strong> iodide test.<br />
Ag + (aq) + Br - (aq) → AgBr(s)<br />
Ag + (aq) + I – (aq) → AgI(s)<br />
5. You are presented with a white solid powder. You suspect that <strong>the</strong> powder could be ei<strong>the</strong>r<br />
potassium iodide or sodium chloride. Expla<strong>in</strong> <strong>the</strong> chemical tests that you would perform <strong>and</strong> <strong>the</strong><br />
order that you would perform <strong>the</strong>m, <strong>to</strong> confirm <strong>the</strong> identity of <strong>the</strong> unknown white powder.<br />
First perform flame test <strong>to</strong> identify <strong>the</strong> metal ion:<br />
lilac flame = potassium; orangey-yellow flame = sodium.<br />
Then confirm <strong>the</strong> non-metal ion us<strong>in</strong>g <strong>the</strong> halide test with silver nitrate:<br />
white precipitate = chloride; yellow precipitate = iodide.<br />
PRACTICAL What’s <strong>the</strong> powder (page 97)<br />
Safety – take care with <strong>the</strong>se practicals <strong>and</strong> ensure that you consult <strong>the</strong> relevant CLEAPSS<br />
guidance.<br />
Silver nitrate is quite expensive, encourage students <strong>to</strong> use spar<strong>in</strong>gly.<br />
This practical could be extended significantly by giv<strong>in</strong>g students a range of common alkali<br />
metal halides <strong>and</strong> ask<strong>in</strong>g <strong>the</strong>m <strong>to</strong> identify all <strong>the</strong> salts (Labelled A, B, C, etc). Ensure that you or<br />
your technician makes a note of which salt is labelled with which letter!<br />
28
WJEC GCSE Additional Science Teacher’s Notes<br />
10<br />
Chemical bond<strong>in</strong>g, structure<br />
<strong>and</strong> properties<br />
_Copper – a metal (pages 99–100)_________________<br />
Questions<br />
1. What are <strong>the</strong> two most important properties of metals<br />
Metals are good conduc<strong>to</strong>rs of heat <strong>and</strong> electricity.<br />
2. What properties make copper such a good material for mak<strong>in</strong>g water pipes<br />
Copper is unreactive, malleable <strong>and</strong> ductile.<br />
3. Why are electrical connect<strong>in</strong>g wires made out of str<strong>and</strong>s of copper<br />
Str<strong>and</strong>s of wire allow <strong>the</strong> connect<strong>in</strong>g leads <strong>to</strong> be much more flexible.<br />
4. Why are metals such good conduc<strong>to</strong>rs of electricity<br />
Metals have a ‘sea’ of negatively charged, free electrons that can easily move throughout <strong>the</strong><br />
structure of <strong>the</strong> metal.<br />
5. Describe how <strong>the</strong> ‘positive ion/free electron’ model of copper can be used <strong>to</strong> expla<strong>in</strong> its physical<br />
properties:<br />
a High melt<strong>in</strong>g <strong>and</strong> boil<strong>in</strong>g po<strong>in</strong>t<br />
The metallic bonds hold<strong>in</strong>g <strong>the</strong> positive metal ions <strong>to</strong>ge<strong>the</strong>r <strong>in</strong> <strong>the</strong>ir lattice structure are<br />
very strong <strong>and</strong> need a lot of heat energy <strong>to</strong> break <strong>the</strong>m.<br />
b Ductility<br />
Although metallic bonds are strong, copper has relatively weaker bonds than o<strong>the</strong>r metals<br />
mak<strong>in</strong>g it quite ductile – <strong>the</strong> bonds can be pulled apart dur<strong>in</strong>g stretch<strong>in</strong>g.<br />
c<br />
Malleability<br />
As (b) but <strong>the</strong> bonds can also be hammered or squashed <strong>in</strong><strong>to</strong> shape.<br />
d Toughness<br />
The fact that <strong>the</strong> copper metallic bonds allow <strong>the</strong>mselves <strong>to</strong> be deformed out of shape<br />
means that <strong>the</strong>y will not fracture (break apart) easily when stressed.<br />
Discussion po<strong>in</strong>t<br />
Your teacher may show you an animation of conduction of electricity <strong>in</strong> a metal. How does <strong>the</strong> conductivity<br />
of a metal change with temperature, <strong>the</strong> dimensions of <strong>the</strong> wire <strong>and</strong> <strong>the</strong> material that <strong>the</strong> wire is made of<br />
An excellent animation <strong>to</strong> use, if you can get hold of a copy of it, is ‘Resistance Simula<strong>to</strong>r’ by<br />
Vibrant Effects Ltd.<br />
On-l<strong>in</strong>e alternatives are:<br />
www.absorblearn<strong>in</strong>g.com/media/item.actionquick=t6<br />
www.absorblearn<strong>in</strong>g.com/media/item.actionquick=11a<br />
29
WJEC GCSE Additional Science Teacher’s Notes<br />
_ Sodium chloride (common salt) – an ionic compound _<br />
(pages 100–102)<br />
Questions<br />
6. How are sodium <strong>and</strong> chloride ions formed from sodium <strong>and</strong> chlor<strong>in</strong>e a<strong>to</strong>ms<br />
Sodium ions form from sodium a<strong>to</strong>ms when <strong>the</strong> outermost electron on <strong>the</strong> sodium a<strong>to</strong>m is<br />
removed. Chloride ions form from chlor<strong>in</strong>e a<strong>to</strong>ms when an extra electron is added <strong>to</strong> its<br />
electron configuration.<br />
7. Why is sodium chloride (common salt) used as a flavour<strong>in</strong>g <strong>and</strong> preservative for food<br />
Our <strong>to</strong>ngues have evolved <strong>to</strong> sense <strong>the</strong> flavour of common salt ‘salt<strong>in</strong>ess’ (along with<br />
bitterness, sweetness <strong>and</strong> sourness). Common salt is used as a food preservative, particularly<br />
with meat or fish, because it draws <strong>the</strong> water moisture out of <strong>the</strong> food (<strong>and</strong> <strong>the</strong> microorganisms<br />
that cause <strong>the</strong> meat <strong>to</strong> go rotten) allow<strong>in</strong>g <strong>the</strong> food <strong>to</strong> be edible for a longer period.<br />
8. Expla<strong>in</strong> why sodium chloride crystals are brittle.<br />
Sodium chloride crystals are brittle because when a stress is applied across <strong>the</strong> crystal <strong>the</strong> ion<br />
layers will shift caus<strong>in</strong>g a fracture.<br />
9. What happens when sodium chloride crystals are added <strong>to</strong> water<br />
When added <strong>to</strong> water, <strong>the</strong> sodium chloride crystal lattice breaks down (dissolves) <strong>and</strong> a<br />
solution of positive sodium ions <strong>and</strong> negative chloride ions is formed.<br />
10. Molten <strong>and</strong> solid sodium chloride conta<strong>in</strong> <strong>the</strong> same sodium <strong>and</strong> chloride ions. Why does molten sodium<br />
chloride conduct electricity, while solid sodium chloride does not conduct electricity.<br />
In solid sodium chloride <strong>the</strong> ions are not free <strong>to</strong> move, yet <strong>in</strong> molten sodium chloride <strong>the</strong>y are<br />
free <strong>to</strong> move (<strong>and</strong> create an electric current).<br />
11. Calcium oxide is ano<strong>the</strong>r ionic compound. Calcium has two electrons <strong>in</strong> its outer shell, <strong>and</strong> oxygen has<br />
six electrons <strong>in</strong> its outer shell. Draw dot <strong>and</strong> cross diagrams <strong>to</strong> show how calcium oxide is formed by<br />
electron transfer from calcium <strong>to</strong> oxygen a<strong>to</strong>ms.<br />
calcium ion, Ca 2+ , 2,8,8 oxygen ion, O 2– , 2,8<br />
12. Draw dot <strong>and</strong> cross diagrams <strong>to</strong> show <strong>the</strong> formation of:<br />
a<br />
Lithium fluoride from<br />
lithium <strong>and</strong> fluor<strong>in</strong>e<br />
lithium ion, Li + , 2,8<br />
fluoride ion, F – , 2,8<br />
30
WJEC GCSE Additional Science Teacher’s Notes<br />
b Sodium sulfide from sodium <strong>and</strong> sulfur<br />
c<br />
Magnesium chloride from magnesium <strong>and</strong> chlor<strong>in</strong>e.<br />
Discussion po<strong>in</strong>t<br />
Salt is <strong>in</strong>credibly important <strong>to</strong> us as human be<strong>in</strong>gs. F<strong>in</strong>d out why our bodies rely on salt so much <strong>and</strong> why it<br />
is important <strong>to</strong> regulate <strong>the</strong> amount of salt that we consume <strong>in</strong> our food.<br />
A good place <strong>to</strong> start <strong>to</strong> search about this <strong>to</strong>pic is:<br />
www.rsc.org/Chemsoc/Chembytes/HotTopics/Salt/whysalt.asp<br />
_ Water – a simple covalent molecule (pages 103–104)_<br />
Questions<br />
13. What is a convalent bond<br />
A covalent bond is formed where two or more a<strong>to</strong>ms share electrons <strong>in</strong> <strong>the</strong>ir electron<br />
configurations.<br />
31
WJEC GCSE Additional Science Teacher’s Notes<br />
14. How is water formed from hydrogen <strong>and</strong> oxygen<br />
The oxygen a<strong>to</strong>m shares one electron from one hydrogen a<strong>to</strong>m <strong>and</strong> ano<strong>the</strong>r electron from a<br />
second hydrogen a<strong>to</strong>m.<br />
15. Why is water a liquid at room temperature<br />
The freez<strong>in</strong>g po<strong>in</strong>t of pure water is 0 °C <strong>and</strong> its boil<strong>in</strong>g po<strong>in</strong>t is 100 °C, room temperature<br />
(10–20 °C) is between <strong>the</strong>se two values hence water is a liquid at <strong>the</strong>se temperatures.<br />
16. Why is water only a poor conduc<strong>to</strong>r of electricity<br />
There are few H + <strong>and</strong> OH – ions <strong>in</strong> pure water – hence <strong>the</strong>re are few charged particles free <strong>to</strong><br />
move <strong>and</strong> so water is a poor conduc<strong>to</strong>r of electricity.<br />
17. Draw dot <strong>and</strong> cross diagrams show<strong>in</strong>g <strong>the</strong> covalent bonds <strong>in</strong> <strong>the</strong> follow<strong>in</strong>g molecules:<br />
a hydrogen chloride c methane<br />
b ammonia<br />
18. Some a<strong>to</strong>ms can form double covalent bonds. In <strong>the</strong>se molecules, each a<strong>to</strong>m shares four electrons (<strong>in</strong><br />
two pairs). Carbon dioxide is an example of a molecule conta<strong>in</strong><strong>in</strong>g double covalent bonds.<br />
Draw dot <strong>and</strong> cross diagrams <strong>and</strong> structural formulae for <strong>the</strong> follow<strong>in</strong>g molecules conta<strong>in</strong><strong>in</strong>g double<br />
covalent bonds:<br />
a sulfur dioxide<br />
b oxygen gas<br />
32
WJEC GCSE Additional Science Teacher’s Notes<br />
Discussion po<strong>in</strong>t<br />
Water is an unusual molecule <strong>in</strong> many ways. F<strong>in</strong>d out some of <strong>the</strong> properties of water that make it different<br />
from o<strong>the</strong>r simple molecular compounds. For example, why does water conduct electricity at all, <strong>and</strong> why<br />
does ice float<br />
There are many places on <strong>the</strong> net <strong>to</strong> f<strong>in</strong>d <strong>answers</strong> <strong>to</strong> <strong>the</strong>se <strong>questions</strong>. This would make an excellent<br />
homework task.<br />
The USGS has a good webpage with some of water’s basic properties:<br />
http://ga.water.usgs.gov/edu/waterproperties.html<br />
_Diamond <strong>and</strong> graphite – giant covalent substances<br />
(pages 104–106)<br />
Questions<br />
19. What is an allotrope<br />
Allotropes are different physical forms of <strong>the</strong> same element. The a<strong>to</strong>ms are <strong>the</strong> same, but <strong>the</strong>y<br />
are arranged <strong>in</strong> different configurations.<br />
20. How are <strong>the</strong> structures of graphite <strong>and</strong> diamond different<br />
In diamond, each carbon a<strong>to</strong>m is bonded <strong>to</strong> four o<strong>the</strong>r carbon a<strong>to</strong>ms with a strong covalent<br />
bond <strong>in</strong> a tetrahedral shape. In graphite, one of <strong>the</strong> bonds is very weak <strong>and</strong> <strong>the</strong> structure is<br />
arranged <strong>in</strong> strong hexagonal layers with <strong>the</strong> weak bond hold<strong>in</strong>g <strong>the</strong> layers <strong>to</strong>ge<strong>the</strong>r.<br />
21. Why do both graphite <strong>and</strong> diamond have very high melt<strong>in</strong>g po<strong>in</strong>ts<br />
The covalent bonds between <strong>the</strong> a<strong>to</strong>ms are very strong so <strong>the</strong>y have very high melt<strong>in</strong>g po<strong>in</strong>ts.<br />
22. Why is diamond hard, yet graphite is soft<br />
The weak bonds between <strong>the</strong> layers of carbon a<strong>to</strong>ms on graphite makes graphite quite soft, <strong>the</strong><br />
tetrahedral bond<strong>in</strong>g of <strong>the</strong> carbon a<strong>to</strong>ms <strong>in</strong> diamond makes diamond very strong.<br />
23. Expla<strong>in</strong> why graphite is a non-metal, yet it conducts electricity.<br />
The weakly bound shared electron between <strong>the</strong> layers of carbon a<strong>to</strong>ms <strong>in</strong> graphite can move<br />
quite easily along <strong>the</strong> layers mak<strong>in</strong>g graphite a ‘semi-conduc<strong>to</strong>r’ along <strong>the</strong>se layers.<br />
Discussion po<strong>in</strong>t<br />
Allotropes can be found <strong>in</strong> o<strong>the</strong>r elements as well. F<strong>in</strong>d out about <strong>the</strong> different allotrope forms of:<br />
phosphorous<br />
oxygen<br />
sulfur<br />
t<strong>in</strong><br />
Phosphorus allotropes: white, black, red <strong>and</strong> violet.<br />
Oxygen allotropes: a<strong>to</strong>mic (s<strong>in</strong>gle), molecular dioxygen (double), ozone (triple), tetraoxygen<br />
(quadruple) <strong>and</strong> solid (six different physical forms known).<br />
Sulfur allotropes: <strong>the</strong>re are many different allotropes of sulfur <strong>in</strong>clud<strong>in</strong>g <strong>the</strong> most common S 8 form.<br />
T<strong>in</strong> allotropes: <strong>the</strong>re are four known allotropes of t<strong>in</strong>, <strong>in</strong>clud<strong>in</strong>g <strong>the</strong> two most common forms, grey<br />
t<strong>in</strong> <strong>and</strong> white t<strong>in</strong>.<br />
33
WJEC GCSE Additional Science Teacher’s Notes<br />
PRACTICAL Mak<strong>in</strong>g molecular models (page 106)<br />
A unit cell is <strong>the</strong> smallest repeat<strong>in</strong>g unit <strong>in</strong> <strong>the</strong> structure of a giant structure.<br />
sodium chloride<br />
unit cell<br />
diamond<br />
unit cell<br />
graphite unit cell<br />
_ Carbon nanotubes (pages 106–107)______________<br />
Questions<br />
24. What are carbon nanotubes<br />
Carbon nanotubes are ano<strong>the</strong>r allotrope of carbon produced when graphite layers form <strong>and</strong> <strong>the</strong>n<br />
roll up <strong>in</strong><strong>to</strong> tubes ra<strong>the</strong>r than be<strong>in</strong>g deposited <strong>in</strong> layers.<br />
25. Why are materials made from carbon nanotubes a good choice for components on a bike<br />
Carbon nanotubes are <strong>in</strong>credibly strong, but very lightweight. This makes <strong>the</strong>m ideal for use on<br />
high performance bicycle components.<br />
26. Why do carbon nanotubes conduct electricity How could <strong>the</strong>y be made <strong>in</strong><strong>to</strong> electrical connections<br />
<strong>in</strong>side electronic devices<br />
Carbon nanotubes are good conduc<strong>to</strong>rs of electricity due <strong>to</strong> <strong>the</strong> free electrons that can move up<br />
<strong>and</strong> down <strong>the</strong> tubes. The tubes could be manufactured <strong>to</strong> behave like electrical wire<br />
connections between electronic components on pr<strong>in</strong>ted circuit boards – with very high<br />
conductivities yet 10 000 times th<strong>in</strong>ner than a human hair!<br />
Discussion po<strong>in</strong>t<br />
Carbon nanotubes are def<strong>in</strong>itely a material for <strong>the</strong> future – can you th<strong>in</strong>k of any good applications for a very<br />
lightweight, <strong>in</strong>credibly strong, electrically conduct<strong>in</strong>g material<br />
Lots of military applications, portable comput<strong>in</strong>g, mobile phones, aerospace eng<strong>in</strong>eer<strong>in</strong>g, etc.<br />
_Smart materials (pages 108–109)________________<br />
Questions<br />
27. What is a ‘smart material’<br />
Smart materials have properties which change reversibly with a change <strong>in</strong> <strong>the</strong>ir surround<strong>in</strong>gs.<br />
28. Expla<strong>in</strong> <strong>the</strong> difference between:<br />
a a <strong>the</strong>rmochromic pigment <strong>and</strong> a pho<strong>to</strong>chromic pigment<br />
A <strong>the</strong>rmochromic pigment changes colour with chang<strong>in</strong>g temperature, whereas a<br />
pho<strong>to</strong>chromic pigment changes colour with chang<strong>in</strong>g light <strong>in</strong>tensity.<br />
34
WJEC GCSE Additional Science Teacher’s Notes<br />
b a shape-memory polymer <strong>and</strong> a shape-memory alloy<br />
Shape memory materials return <strong>to</strong> <strong>the</strong>ir orig<strong>in</strong>al shape once deformed when heated. Shapememory<br />
polymers are made of ‘plastic’ materials whereas shape-memory alloys are metals.<br />
29. How can hydrogels be made <strong>to</strong> absorb more or less water<br />
By chang<strong>in</strong>g <strong>the</strong>ir temperature or pH.<br />
30. Expla<strong>in</strong> why smart materials are used <strong>to</strong> manufacture:<br />
a pho<strong>to</strong>chromic flexi glasses<br />
Pho<strong>to</strong>chromic flexi glasses – can be bent out of shape yet returned <strong>to</strong> <strong>the</strong>ir orig<strong>in</strong>al shape<br />
<strong>and</strong> get darker as <strong>the</strong> <strong>in</strong>tensity of <strong>the</strong> sunlight <strong>in</strong>creases.<br />
b sport gum-shields<br />
Sport gum-shields – can be heated <strong>to</strong> allow <strong>the</strong>m <strong>to</strong> be fitted snuggly <strong>to</strong> <strong>the</strong> teeth, <strong>and</strong> <strong>the</strong>n<br />
cooled <strong>to</strong> reta<strong>in</strong> <strong>the</strong> shape. If <strong>the</strong> gum-shield needs <strong>to</strong> be re-fitted it can simply be heated<br />
up, returned <strong>to</strong> its orig<strong>in</strong>al shape <strong>and</strong> <strong>the</strong>n re-fitted <strong>to</strong> <strong>the</strong> teeth.<br />
c<br />
battery power <strong>in</strong>dica<strong>to</strong>rs<br />
Battery power <strong>in</strong>dica<strong>to</strong>rs – a <strong>the</strong>rmochromic pigment can be mixed with a conduct<strong>in</strong>g<br />
substrate <strong>and</strong> ‘pa<strong>in</strong>ted’ on<strong>to</strong> <strong>the</strong> side of a battery. When f<strong>in</strong>gers complete <strong>the</strong> circuit a small<br />
current flows through <strong>the</strong> conduct<strong>in</strong>g substrate which heats up <strong>the</strong> <strong>the</strong>rmochromic pa<strong>in</strong>t<br />
caus<strong>in</strong>g it <strong>to</strong> change colour – more current, more heat, different colours.<br />
d novelty T-shirts<br />
T-shirts that change colour due <strong>to</strong> changes <strong>in</strong> body or surround<strong>in</strong>g temperature or changes<br />
<strong>in</strong> <strong>the</strong> ambient light <strong>in</strong>tensity.<br />
35
WJEC GCSE Additional Science Teacher’s Notes<br />
11<br />
Rates of reaction <strong>and</strong><br />
chemical calculations<br />
_Measur<strong>in</strong>g <strong>the</strong> rate of a reaction (pages 111–15)_____<br />
PRACTICAL Measur<strong>in</strong>g rates of reaction (pages 112–15)<br />
Safety: make sure you consult <strong>the</strong> relevant CLEAPSS guidance before conduct<strong>in</strong>g this practical<br />
work.<br />
Measur<strong>in</strong>g reactions <strong>in</strong>volv<strong>in</strong>g gases<br />
1. What is <strong>the</strong> shape of your graph<br />
The graph will be a positive curve with a decreas<strong>in</strong>g positive gradient.<br />
2. What does your graph tell you Where is <strong>the</strong> rate of reaction fastest<br />
The rate of reaction is highest at <strong>the</strong> start of <strong>the</strong> reaction <strong>and</strong> it gradually decreases with<br />
time.<br />
3. Can you tell when <strong>the</strong> reaction is complete<br />
The reaction is complete when <strong>the</strong> volume of gas produced stays constant for a period of<br />
time.<br />
4. Calculate <strong>the</strong> rate of reaction at <strong>the</strong> steepest part of your graph by draw<strong>in</strong>g a tangent l<strong>in</strong>e <strong>and</strong><br />
measur<strong>in</strong>g <strong>the</strong> gradient (<strong>the</strong> units will be cm 3 /s).<br />
Student measurements from <strong>the</strong>ir own graph.<br />
5. Repeat <strong>the</strong> rate of reaction calculations for both methods. Are <strong>the</strong> rates of reaction <strong>the</strong> same<br />
Should <strong>the</strong>y be <strong>the</strong> same Why might <strong>the</strong> two rates be different<br />
The rates of reaction are likely <strong>to</strong> be similar – <strong>the</strong>y should be <strong>the</strong> same, but <strong>the</strong>re may be<br />
differences due <strong>to</strong> more or less ambient air <strong>in</strong> <strong>the</strong> tubes, friction <strong>in</strong> <strong>the</strong> gas syr<strong>in</strong>ge, leaks,<br />
etc.<br />
Measur<strong>in</strong>g reactions <strong>in</strong>volv<strong>in</strong>g changes of mass<br />
6. What is <strong>the</strong> shape of your graph<br />
The graph will be a negative curve with decreas<strong>in</strong>g negative gradient.<br />
7. What does your graph tell you Where is <strong>the</strong> rate of reaction fastest<br />
The rate of reaction is highest at <strong>the</strong> start of <strong>the</strong> reaction <strong>and</strong> it gradually decreases with<br />
time.<br />
8. Can you tell when <strong>the</strong> reaction is complete<br />
The reaction is complete when <strong>the</strong> mass of <strong>the</strong> system stays stays constant for a period of<br />
time.<br />
36
WJEC GCSE Additional Science Teacher’s Notes<br />
9. Calculate <strong>the</strong> rate of reaction at <strong>the</strong> steepest part of your graph by draw<strong>in</strong>g a tangent l<strong>in</strong>e <strong>and</strong><br />
measur<strong>in</strong>g <strong>the</strong> gradient (<strong>the</strong> units will be g/s).<br />
Student measurements from <strong>the</strong>ir own graph.<br />
Measur<strong>in</strong>g reactions <strong>in</strong>volv<strong>in</strong>g changes of ligh transmission through a<br />
precipitate<br />
10. What is <strong>the</strong> pattern/shape of your graph<br />
The graph will be a negative curve with decreas<strong>in</strong>g negative gradient.<br />
11. What does your graph tell you Where is <strong>the</strong> rate of reaction fastest<br />
The rate of reaction is highest at <strong>the</strong> start of <strong>the</strong> reaction <strong>and</strong> it gradually decreases with<br />
time.<br />
12. Can you tell when <strong>the</strong> reaction is complete<br />
The reaction is complete when <strong>the</strong> light transmission of <strong>the</strong> system stays constant for a<br />
period of time.<br />
Questions<br />
1. What is meant by <strong>the</strong> rate of a reaction<br />
How much reaction product is produced <strong>in</strong> a set time.<br />
2. Expla<strong>in</strong> how you use a graph <strong>to</strong> measure <strong>the</strong> rate of a reaction.<br />
Draw a tangent l<strong>in</strong>e <strong>to</strong> <strong>the</strong> reaction curve at any po<strong>in</strong>t <strong>in</strong> time – <strong>the</strong> rate of reaction is <strong>the</strong><br />
gradient (slope) of <strong>the</strong> l<strong>in</strong>e.<br />
3. How can you tell from a rate of reaction graph where <strong>the</strong> reaction is:<br />
a fastest<br />
The rate of reaction is fastest where <strong>the</strong> gradient is biggest (where <strong>the</strong> slope is steepest).<br />
b complete<br />
The reaction is complete where <strong>the</strong> graph is horizontal, when <strong>the</strong> gradient is zero.<br />
4. In a calcium carbonate <strong>and</strong> hydrochloric acid experiment, a student collects <strong>the</strong> carbon dioxide gas <strong>and</strong><br />
produces <strong>the</strong> rate of reaction graph shown <strong>in</strong> Figure 11.10. On a copy of this graph, sketch <strong>the</strong> graph<br />
you would expect from similar experiments carried out with:<br />
a acid of twice <strong>the</strong> concentration, but at <strong>the</strong> same temperature<br />
The rate of reaction will be <strong>the</strong> same, as this is limited by <strong>the</strong> concentration of <strong>the</strong> acid not<br />
<strong>the</strong> amount.<br />
b <strong>the</strong> same amount of each chemical, but carried out at a higher temperature.<br />
A higher temperature means a faster rate of reaction, but as <strong>the</strong> amount of chemicals is<br />
fixed, <strong>the</strong> f<strong>in</strong>al volume of gas will be <strong>the</strong> same.<br />
37
WJEC GCSE Additional Science Teacher’s Notes<br />
_ The importance of catalysts (pages 117–120)______<br />
Questions<br />
5. What is a catalyst<br />
Catalysts are substances that <strong>in</strong>crease <strong>the</strong> rate of a chemical reaction but rema<strong>in</strong> chemically<br />
unchanged at <strong>the</strong> end of <strong>the</strong> reaction.<br />
6. How can <strong>the</strong> rate of reaction of calcium carbonate with hydrochloric acid be <strong>in</strong>creased<br />
Increase <strong>the</strong> surface area of <strong>the</strong> calcium carbonate (powder)<br />
Increase <strong>the</strong> concentration of <strong>the</strong> hydrochloric acid<br />
Increase <strong>the</strong> temperature of <strong>the</strong> reaction<br />
Use a suitable catalyst<br />
7. When magnesium reacts with hydrochloric acid, hydrogen gas is produced. In a particular experiment<br />
at 20 °C, 50 cm 3 of hydrogen gas was produced <strong>in</strong> 3 m<strong>in</strong>utes. What would be <strong>the</strong> result of <strong>the</strong> reaction if<br />
<strong>the</strong> same quantities of reactant were used but <strong>the</strong> reaction was carried out at 30 °C<br />
The same amount of hydrogen gas would be produced (50 cm 3 ) but <strong>the</strong> rate of reaction would<br />
be faster – it would produce <strong>the</strong> same amount of gas <strong>in</strong> less time.<br />
8. Why is it important <strong>to</strong> a chemical company <strong>to</strong> <strong>in</strong>crease <strong>the</strong> yield of a reaction<br />
Increas<strong>in</strong>g <strong>the</strong> yield of a reaction creates more profit – <strong>the</strong> company can make <strong>and</strong> sell more<br />
product for <strong>the</strong> same amount of reactants.<br />
9. Why is it important for <strong>the</strong> environment <strong>to</strong> use catalysts <strong>in</strong> <strong>the</strong> production of chemicals<br />
Catalysts reduce <strong>the</strong> amount of energy required <strong>to</strong> produce chemical products which <strong>in</strong> turn<br />
preserves world fuel reserves <strong>and</strong> also reduces <strong>the</strong> environmental impact of burn<strong>in</strong>g fossil fuels<br />
<strong>and</strong> its effect on <strong>the</strong> greenhouse effect <strong>and</strong> global warm<strong>in</strong>g.<br />
Discussion po<strong>in</strong>t<br />
The Haber Process is <strong>in</strong>credibly important <strong>to</strong> <strong>the</strong> whole of <strong>the</strong> world’s population. Not only is a catalyst used<br />
for <strong>the</strong> reaction between nitrogen <strong>and</strong> hydrogen, but <strong>the</strong> process is optimised by adjust<strong>in</strong>g <strong>the</strong> temperature<br />
<strong>and</strong> pressure of <strong>the</strong> reaction.<br />
Your teacher will show you an animation of <strong>the</strong> process where you can adjust <strong>the</strong> temperature <strong>and</strong> pressure<br />
of <strong>the</strong> reaction. F<strong>in</strong>d out <strong>the</strong> conditions <strong>to</strong> produce <strong>the</strong> optimum yield.<br />
www.freezeray.com/flashFiles/<strong>the</strong>HaberProcess.htm<br />
Use <strong>the</strong> <strong>in</strong>structions given on <strong>the</strong> website above, or use ano<strong>the</strong>r suitable animation. Generally, <strong>the</strong><br />
pressure of <strong>the</strong> reaction is about 200 atm <strong>and</strong> <strong>the</strong> temperature is about 450 °C.<br />
TASK Simulat<strong>in</strong>g rates of reaction (page 119)<br />
There are many different commercial <strong>and</strong> web-based rate of reaction simula<strong>to</strong>rs available. The<br />
one shown <strong>in</strong> Figure 11.15 is particularly user-friendly <strong>and</strong> can be obta<strong>in</strong>ed via:<br />
www.focuseducational.com/product/science-<strong>in</strong>vestigations-1/40<br />
This task would be best carried out <strong>in</strong>dividually on a school computer network where <strong>the</strong>re is<br />
direct access <strong>to</strong> Excel.<br />
38
WJEC GCSE Additional Science Teacher’s Notes<br />
PRACTICAL Investigat<strong>in</strong>g <strong>the</strong> rate of a reaction<br />
(pages 119–120)<br />
Give students a suitable range of reactions <strong>to</strong> <strong>in</strong>vestigate – you could have different groups<br />
do<strong>in</strong>g different reactions <strong>and</strong> different fac<strong>to</strong>rs <strong>the</strong>n pool<strong>in</strong>g <strong>the</strong> results. This Practical (<strong>and</strong> its<br />
report outcome) has been deliberately left open <strong>to</strong> suit local conditions <strong>and</strong> time constra<strong>in</strong>ts.<br />
_Chemical calculations (pages 120–29)_____________<br />
Questions<br />
10. Calculate <strong>the</strong> relative molecular mass, M r , for <strong>the</strong> follow<strong>in</strong>g molecules.<br />
a oxygen gas, O 2 = [16 + 16] = 32<br />
b sulfur dioxide, SO 2 = [32 + (2 × 16)] = 64<br />
c methane, CH 4 = [12 + (4 × 1)] = 16<br />
d nitrogen dioxide, NO 2 = [14 + (2 × 16)] = 46<br />
e carbon tetrachloride, CCl 4 = [12 + (4 × 35.5)] = 154<br />
f ammonia, NH 3 = [14 + (3 × 1)] = 17<br />
g ethane, C 2 H 6 = [(2 × 12) + (6 × 1)] = 30<br />
11. Calculate <strong>the</strong> relative formular mass of <strong>the</strong> follow<strong>in</strong>g ionic compounds.<br />
a lithium chloride, LiCl = [7 + 35.5] = 42.5<br />
b potassium oxide, K 2 O = [(2 × 39) + 16] = 94<br />
c sodium sulfide, Na 2 S = [(2 × 23) + 32] = 78<br />
d magnesium carbonate, MgCO 3 = [24 + 12 + (3 × 16)] = 84<br />
e calcium nitrate, Ca(NO 3 ) 2 = [40 + (2 × (14 + (3 × 16)))] = 164<br />
f beryllium oxide, BeO = [9 + 16] = 25<br />
g rubidium carbonate, Rb 2 CO 3 = [(2 × 85) + 12 + (3 × 16)] = 230<br />
h ammonium sulfate, (NH 4 ) 2 SO 4 = [(2 × (14 + (4 × 1))) + 32 + (4 × 16)] = 132<br />
12. Calculate <strong>the</strong> percentage composition of each molecule or compound <strong>in</strong> Questions 10 <strong>and</strong> 11.<br />
Molecules <strong>in</strong> Question 10:<br />
a oxygen gas, O 2<br />
100 % oxygen<br />
b sulfur dioxide, SO 2<br />
50 % sulfur, 50 % oxygen<br />
c methane, CH 4 75 % carbon, 25 % hydrogen<br />
d nitrogen dioxide, NO 2 30.4 % nitrogen, 69.6 % oxygen<br />
e carbon tetrachloride, CCl 4 7.8 % carbon, 92.2 % chlor<strong>in</strong>e<br />
f ammonia, NH 3 82.4 % nitrogen, 17.6 % hydrogen<br />
g ethane, C 2 H 6<br />
80 % carbon, 20 % hydrogen<br />
39
WJEC GCSE Additional Science Teacher’s Notes<br />
Ionic compounds <strong>in</strong> Question 11:<br />
a lithium chloride, LiCl 16.5 % lithium, 83.5 % chlor<strong>in</strong>e<br />
b potassium oxide, K 2 O 83 % potassium, 17 % oxygen<br />
c sodium sulfide, Na 2 S 59 % sodium, 41 % sulfur<br />
d magnesium carbonate, MgCO 3 28.6 % magnesium, 14.3 % carbon, 57.1 % oxygen<br />
e calcium nitrate, Ca(NO 3 ) 2 24.4 % calcium, 17.1 % nitrogen, 58.5 % oxygen<br />
f beryllium oxide, BeO 36 % beryllium, 64 % oxygen<br />
g rubidium carbonate, Rb 2 CO 3 73.9 % rubidium, 5.2 % carbon, 20.9 % oxygen<br />
h ammonium sulfate, (NH 4 ) 2 SO 4 21.2 % nitrogen, 6.1 % hydrogen, 24.2% sulfur, 48.5 %<br />
oxygen<br />
13. Calculate <strong>the</strong> <strong>to</strong>tal mass of reactants <strong>and</strong> products <strong>in</strong> <strong>the</strong> follow<strong>in</strong>g reactions:<br />
a N 2 (g) + 3H 2 (g) → 2NH 3 (g)<br />
Reactants: (2 × 14) + 3 × (2 × 1) = 34<br />
Products: 2 × (14 + (3 × 1)) = 34<br />
b 2H 2 (g) + O 2 (g) → 2H 2 O (g)<br />
c<br />
Reactants: 2 × (2 × 1) + (2 × 16) = 36<br />
Products: 2 × ((2 × 1) + 16) = 36<br />
Mg (s) + H 2 SO 4 (aq) → MgSO 4 (aq) + H 2 O (g)<br />
Reactants: 24 + ((2 × 1) + 32 + (4 × 16)) = 122<br />
Products: (24 + 32 + (4 × 16)) + (2 × 1) = 122<br />
d NaOH (aq) + HNO 3 (aq) → NaNO 3 (aq) + H 2 (l)<br />
Reactants: (23 + 16 + 1) + (1 + 14 + (3 × 16)) = 103<br />
Products: (23 + 14 + (3 × 16) + ((2 × 1) +16) = 103<br />
14. Calculate <strong>the</strong> mass of calcium oxide formed by <strong>the</strong> complete decomposition of 5 kg of calcium<br />
carbonate.<br />
CaCO 3 (s) → CaO (s) + CO 2 (g)<br />
Relative formula mass of calcium carbonate = 40 + 12 + (3 × 16) = 100<br />
Relative formula mass of calcium oxide = 40 + 16 = 56<br />
So 100 g of calcium carbonate makes 56 g of calcium oxide<br />
1 g of calcium carbonate makes (56/100) = 0.56 g of calcium oxide<br />
5 kg = 5000 g of calcium carbonate makes 5000 × 0.56 = 2800 g of calcium oxide = 2.8 kg<br />
15. Calculate <strong>the</strong> mass of sodium chloride that can be formed from <strong>the</strong> neutralisation of 8 kg of sodium<br />
hydroxide with hydrochloric acid.<br />
NaOH (aq) + HCl (aq) → NaCl (aq) + H 2 O (l)<br />
Relative formula mass of sodium hydroxide = 23 + 16 + 1 = 40<br />
Relative formula mass of sodium chloride = 23 + 35 = 58<br />
So 40 g of sodium hydroxide makes 58 g of sodium chloride<br />
1 g of sodium hydroxide makes (58/40) = 1.45 g of sodium chloride<br />
8 g of sodium hydroxide makes 8 x 1.45 = 11.6 g of sodium chloride<br />
40
WJEC GCSE Additional Science Teacher’s Notes<br />
16. Calculate <strong>the</strong> mass of calcium chloride that can be formed by <strong>the</strong> reaction of 3 g of calcium cabonate<br />
with an excess of hydrochloric acid.<br />
CaCO 3 (s) + 2HCl (aq) → CaCl 2 (aq) + H 2 O (l) + CO 2 (g)<br />
Relative formula mass of calcium carbonate = 40 + 12 + (3 × 16) = 100<br />
Relative formula mass of calcium chloride = 40 + (2 × 35) = 110<br />
So 100 g of calcium carbonate makes 110 g of calcium chloride<br />
1 g of calcium carbonate makes (110/100) = 1.1 g of calcium chloride<br />
3 g of calcium carbonate makes 3 × 1.1 = 3.3 g of calcium chloride<br />
PRACTICAL Calculat<strong>in</strong>g <strong>the</strong> formula of copper(II) oxide<br />
(pages 124–25)<br />
Safety: make sure you consult <strong>the</strong> relevant CLEAPSS guidance before conduct<strong>in</strong>g this practical<br />
work.<br />
Answers <strong>to</strong> Questions 1–5 will depend on <strong>the</strong> Students’ results. The ratio should be<br />
approximately 1:1.<br />
PRACTICAL Calculat<strong>in</strong>g <strong>the</strong> formula of magnesium oxide<br />
(pages 125–26)<br />
Safety: make sure you consult <strong>the</strong> relevant CLEAPSS guidance before conduct<strong>in</strong>g this practical<br />
work.<br />
Answers <strong>to</strong> Questions 1–5 will depend on <strong>the</strong> Students’ results. The ratio should be<br />
approximately 1:1.<br />
Questions<br />
17. Calculate <strong>the</strong> percentage yield for <strong>the</strong> Practical Calculat<strong>in</strong>g <strong>the</strong> formula of magnesium oxide (pages<br />
125–6).<br />
Answers will depend on Students’ results from <strong>the</strong> Practical.<br />
18. Six <strong>to</strong>nnes of ethanol is produced from 15 <strong>to</strong>nnes of e<strong>the</strong>ne when it is reacted with an excess of water.<br />
Calculate <strong>the</strong> percentage yield of <strong>the</strong> reaction.<br />
C 2 H 4 (g) + H 2 O (g) → C 2 H 5 OH (g)<br />
Relative molecular mass of e<strong>the</strong>ne = (2 × 12) + (4 × 1) = 28<br />
Relative molecular mass of ethanol = (2 × 12) + (6 × 1) + 16 = 46<br />
So 28 <strong>to</strong>nnes of e<strong>the</strong>ne produces 46 <strong>to</strong>nnes of ethanol<br />
1 <strong>to</strong>nne of e<strong>the</strong>ne produces (46/28) = 1.64 <strong>to</strong>nnes of ethanol<br />
15 <strong>to</strong>nnes of e<strong>the</strong>ne produces (15 × 1.64) = 24.6 <strong>to</strong>nnes of ethanol<br />
Percentage yield<br />
6<br />
100<br />
24.4 %<br />
24.6<br />
19. F<strong>in</strong>d <strong>the</strong> percentage yield of <strong>the</strong> reaction if 5 g of CO 2 is realised from <strong>the</strong> decomposition of 10 g of<br />
CaCO 3 .<br />
CaCO 3 (s) → CaO (s) + CO 2 (g)<br />
41
WJEC GCSE Additional Science Teacher’s Notes<br />
Relative formula mass of calcium carbonate = 40 + 12 + (3 × 16) = 100<br />
Relative formula mass of calcium oxide = 40 + 16 = 56<br />
So 100 g of calcium carbonate makes 56 g of calcium oxide.<br />
1 g of calcium carbonate makes 0.56 g of calcium oxide<br />
10 g of calcium carbonate makes 5.6 g of calcium oxide<br />
Percentage yield<br />
5<br />
100<br />
89.3 %<br />
5.6<br />
20. The combustion of ethanol: C 2 H 5 OH (l) + 3O 2 (g) → 2CO 2 (g) + 3H 2 O (g).<br />
Bonds broken:<br />
5 × C–H = (5 × 412) = 2060 kJ<br />
1 × C–C = (1 × 348) = 348 kJ<br />
1 × C–O = (1 × 358) = 358 kJ<br />
1 × O–H = (1 × 463) = 463 kJ<br />
Total energy <strong>in</strong> = 3229 kJ<br />
Bonds made:<br />
4 × C=O = (4 × 743) = 2972 kJ<br />
6 × O–H = (6 × 463) = 2778 kJ<br />
Total energy out = 5750 kJ<br />
Heat of combustion = 5750 – 3229 = 2521 kJ – EXOTHERMIC<br />
21. The neutralisation of sodium hydroxide by hydrochloric acid:<br />
HCl (aq) + NaOH (aq) → NaCl (aq) + H 2 O (l)<br />
ERRATUM Calculation Error: The neutralisation reaction of sodium hydroxide by<br />
hydrochloric acid is exo<strong>the</strong>rmic.<br />
22. The reaction of lithium with water: 2Li (s) + H 2 O (l) → 2LiOH (aq) + H 2 (g)<br />
ERRATUM Calculation Error: The reaction of lithium with water is exo<strong>the</strong>rmic.<br />
23. The reaction of nitrogen <strong>and</strong> oxygen gas: N 2 (g) + O 2 (g) → 2NO (g)<br />
Bonds broken:<br />
1 × NN = 1 × 944 = 944<br />
1 × O=O = 1 × 496 = 496<br />
Total energy <strong>in</strong> = 1440 kJ<br />
Bonds made:<br />
2 × NO = 2 × 627 = 1254 kJ<br />
Total energy out = 1254 kJ<br />
Heat of reaction = 1254 – 1440 = –186 kJ – ENDOTHERMIC<br />
42
WJEC GCSE Science Teacher’s Notes<br />
12<br />
Organic chemistry<br />
_Alkanes <strong>and</strong> alkenes (pages 132–35)______________<br />
PRACTICAL Mak<strong>in</strong>g alkenes from alkanes<br />
(pages 133–34)<br />
This experiment is based on a practical from <strong>the</strong> Royal Society’s ‘Practical chemistry’ website<br />
www.practicalchemistry.org/experiments/crack<strong>in</strong>g-hydrocarbons,139,EX.html. Technical <strong>notes</strong><br />
are available from <strong>the</strong> l<strong>in</strong>k above.<br />
Questions<br />
1. Look at <strong>the</strong> structural formula <strong>in</strong> Figure 12.5. Is this chemical an alkane or an alkene Give a reason for<br />
your answer.<br />
It is an alkene because it has a carbon-carbon double bond.<br />
2. Alkenes are more reactive than alkanes. Suggest a reason for this, us<strong>in</strong>g your knowledge of <strong>the</strong>ir<br />
chemical structure.<br />
The double bond can be broken quite easily <strong>to</strong> attach <strong>to</strong> ano<strong>the</strong>r a<strong>to</strong>m. The structure of an<br />
alkane is more stable.<br />
_What’s <strong>the</strong> difference between a <strong>the</strong>rmoplastic <strong>and</strong> a<br />
<strong>the</strong>rmoset (pages 136–37)<br />
TASK Why use this plastic (page 137)<br />
The <strong>answers</strong> <strong>to</strong> this task will depend on <strong>the</strong> plastic item chosen by <strong>the</strong> pupil.<br />
44
WJEC GCSE Additional Science Teacher’s Notes<br />
13<br />
Water<br />
_How do we get clean water (pages 138–42)________<br />
Questions<br />
1. In areas of <strong>the</strong> world where <strong>the</strong> dr<strong>in</strong>k<strong>in</strong>g water is not fully treated, or when <strong>the</strong> water is thought <strong>to</strong> have<br />
been contam<strong>in</strong>ated, people are asked <strong>to</strong> boil <strong>the</strong> water for several m<strong>in</strong>utes <strong>and</strong> <strong>the</strong>n cool it before<br />
dr<strong>in</strong>k<strong>in</strong>g it. Suggest <strong>the</strong> reason for this.<br />
Boil<strong>in</strong>g will kill many of <strong>the</strong> bacteria which may be <strong>in</strong> <strong>the</strong> water.<br />
2. Suggest five ways <strong>in</strong> which an average home could reduce <strong>the</strong> amount of water used per day.<br />
Possible suggestions:<br />
Have a shower ra<strong>the</strong>r than a bath.<br />
Don’t leave <strong>the</strong> tap runn<strong>in</strong>g (e.g. when clean<strong>in</strong>g your teeth).<br />
Use economy flush on <strong>the</strong> <strong>to</strong>ilet (where fitted) or put a brick <strong>in</strong> <strong>the</strong> cistern.<br />
Restrict <strong>the</strong> use of a hose <strong>to</strong> water <strong>the</strong> garden.<br />
Don’t wash <strong>the</strong> car <strong>to</strong>o often.<br />
Collect ra<strong>in</strong>water <strong>to</strong> use for wash<strong>in</strong>g up or water<strong>in</strong>g <strong>the</strong> garden.<br />
Ma<strong>in</strong>ta<strong>in</strong> taps so that <strong>the</strong>y don’t drip.<br />
Five is quite a lot of ways <strong>to</strong> th<strong>in</strong>k of. This is deliberate, <strong>to</strong> promote some lateral th<strong>in</strong>k<strong>in</strong>g.<br />
Discussion po<strong>in</strong>t<br />
The water on <strong>the</strong> planet is constantly recycled by <strong>the</strong> water cycle, so why do we need <strong>to</strong> conserve water, if<br />
what we use eventually f<strong>in</strong>ds its way back <strong>to</strong> rivers <strong>and</strong> reservoirs<br />
There would be no need <strong>to</strong> conserve water if more of it was accessible <strong>and</strong> if it was evenly<br />
distributed, both <strong>in</strong> space <strong>and</strong> time. Po<strong>in</strong>ts <strong>to</strong> consider:<br />
A lot of <strong>the</strong> water is salt water <strong>in</strong> seas <strong>and</strong> oceans. This is not easily available for direct use by<br />
humans.<br />
Only about 1% of <strong>the</strong> world’s fresh water supply is accessible for direct use. Much of <strong>the</strong> rest<br />
is deep underground or <strong>in</strong> <strong>in</strong>accessible areas (e.g. polar ice).<br />
Some areas of <strong>the</strong> world have plentiful water, whereas o<strong>the</strong>r areas have <strong>in</strong>sufficient. Transport<br />
of water across <strong>the</strong> globe is difficult (<strong>and</strong> virtually impossible <strong>in</strong> <strong>the</strong> quantities needed <strong>in</strong> dry<br />
areas).<br />
Ra<strong>in</strong>fall is seasonal. Water may have <strong>to</strong> be conserved <strong>in</strong> <strong>the</strong> wetter periods for use <strong>in</strong> dryer<br />
seasons. Water is particularly important dur<strong>in</strong>g crop grow<strong>in</strong>g seasons, as this requires large<br />
amounts of water.<br />
Question<br />
3. F<strong>in</strong>d out why dr<strong>in</strong>k<strong>in</strong>g salt water dehydrates you.<br />
If cells come <strong>in</strong><strong>to</strong> contact with a solution which is more concentrated than <strong>the</strong>ir cy<strong>to</strong>plasm, <strong>the</strong>y<br />
will lose water by osmosis. Students will cover osmosis <strong>in</strong> <strong>the</strong> biology section.<br />
45
WJEC GCSE Additional Science Teacher’s Notes<br />
PRACTICAL Separat<strong>in</strong>g ethanol <strong>and</strong> water (page 141)<br />
Evaluate this method of separat<strong>in</strong>g ethanol <strong>and</strong> water. Are <strong>the</strong>re any improvements that could be made<br />
<strong>to</strong> <strong>the</strong> experimental method<br />
The ma<strong>in</strong> problem is us<strong>in</strong>g a Bunsen burner <strong>to</strong> heat <strong>the</strong> mixture <strong>to</strong> 78 °C. The temperature will<br />
often exceed that <strong>and</strong> will be difficult <strong>to</strong> ma<strong>in</strong>ta<strong>in</strong>. As only ethanol <strong>and</strong> water are present, this is<br />
not a huge problem, but a <strong>the</strong>rmostatic water bath would be better.<br />
_How can we identify substances <strong>in</strong> a solution_______<br />
(pages 142–44)<br />
PRACTICAL Who wrote <strong>the</strong> note (page 144)<br />
Preparation of <strong>in</strong>k samples:<br />
You need at least two (preferably three) <strong>in</strong>k samples that are different <strong>in</strong> composition. It is<br />
essential that only one of samples B, C <strong>and</strong> D matches A, but it would not matter if <strong>the</strong> o<strong>the</strong>r<br />
two samples were <strong>the</strong> same. The <strong>in</strong>ks can be found by simply try<strong>in</strong>g different pens, or by<br />
construct<strong>in</strong>g <strong>the</strong> samples us<strong>in</strong>g mixtures of <strong>in</strong>ks.<br />
_What is gas chroma<strong>to</strong>graphy (pages 145–46)______<br />
TASK How is solubility affected by temperature<br />
(pages 145–46)<br />
This exercise will stretch more able pupils <strong>and</strong> will probably be <strong>to</strong>o complex for lower ability<br />
pupils.<br />
1. How much sodium nitrate can dissolve <strong>in</strong> water at 30 °C<br />
95 g/100 cm 3 water<br />
2. Which compound is <strong>the</strong> least soluble at 50 °C<br />
Potassium chlorate<br />
3. Which compound’s solubility is least affected by temperature<br />
Sodium chloride<br />
4. How much extra potassium iodide can dissolve <strong>in</strong> 100 cm 3 of water if <strong>the</strong> temperature is <strong>in</strong>creased<br />
from 15 °C <strong>to</strong> 30 °C<br />
25 g/100 cm 3<br />
5. Are <strong>the</strong> follow<strong>in</strong>g solutions unsaturated, saturated or supersaturated<br />
a 40 g/100 cm 3 sodium chloride at 75 °C<br />
Saturated<br />
46
WJEC GCSE Additional Science Teacher’s Notes<br />
b 2 g/100 cm 3 potassium chlorate at 45 °C<br />
Unsaturated<br />
c 155 g/100 cm 3 potassium iodide at 15 °C Saturated<br />
d 100 g/100 cm 3 sodium nitrate at 30 °C Supersaturated<br />
Note that pupils are not required <strong>to</strong> recall any <strong>in</strong>formation about supersaturated solutions.<br />
The <strong>in</strong>formation is <strong>in</strong>cluded here <strong>to</strong> test <strong>in</strong>terpretation of <strong>the</strong> data.<br />
6. Compare <strong>the</strong> solubility curves for potassium iodide <strong>and</strong> potassium nitrate.<br />
Potassium iodide is more soluble than potassium nitrate over <strong>the</strong> whole range of<br />
temperatures.<br />
The solubility of both substances <strong>in</strong>creases with temperature.<br />
The solubility of potassium iodide <strong>in</strong>creases at a constant rate (approx. 15 g/100 cm 3 for<br />
every 10 °C), whereas <strong>the</strong> solubility of potassium nitrate <strong>in</strong>creases at a greater rate as <strong>the</strong><br />
temperature <strong>in</strong>creases.<br />
_What makes water hard or soft (pages 147–49)____<br />
PRACTICAL How can we tell <strong>the</strong> difference between<br />
hard <strong>and</strong> soft water (pages 147–48)<br />
It is envisaged here that four different water samples are made up <strong>in</strong> <strong>the</strong> follow<strong>in</strong>g ways:<br />
soft water – e.g. deionised water<br />
permanent hard water – e.g. us<strong>in</strong>g MgSO 4<br />
temporary hard water – e.g. made by bubbl<strong>in</strong>g CO 2 <strong>in</strong><strong>to</strong> lime water until <strong>the</strong> <strong>in</strong>itial<br />
precipitate just clears<br />
water sample with a mixture of permanent <strong>and</strong> temporary hardness.<br />
1. Use your results <strong>to</strong> describe <strong>the</strong> hardness of each water sample, <strong>and</strong> whe<strong>the</strong>r this hardness is<br />
temporary or permanent. Expla<strong>in</strong> <strong>the</strong> reasons for your identification.<br />
The answer will depend on <strong>the</strong> labell<strong>in</strong>g of solutions <strong>and</strong> possibly <strong>the</strong> results. Temporary<br />
hard water should be identified as removable by boil<strong>in</strong>g.<br />
2. This method works fairly successfully for compar<strong>in</strong>g <strong>the</strong> hardness of <strong>the</strong> water samples. Suggest an<br />
improvement that could be made if you wanted a more accurate measure of water hardness.<br />
It would be necessary <strong>to</strong> use water samples of known hardness <strong>and</strong> <strong>to</strong> draw a calibration<br />
curve <strong>to</strong> enable <strong>the</strong> results <strong>to</strong> be related <strong>to</strong> actual hardness.<br />
TASK Is hard water good for your health (page 149)<br />
2. Why do you th<strong>in</strong>k <strong>the</strong> fact that hard water areas of <strong>the</strong> world tend <strong>to</strong> have lower rates of heart<br />
disease than soft water areas is considered ra<strong>the</strong>r weak evidence for <strong>the</strong> hypo<strong>the</strong>sis that dr<strong>in</strong>k<strong>in</strong>g<br />
hard water reduces heart disease<br />
<br />
<br />
<br />
The areas (both hard water <strong>and</strong> soft water) are likely <strong>to</strong> be very different from each o<strong>the</strong>r<br />
so a truly ‘fair test’ is not possible.<br />
The differences are small.<br />
The results of different studies are variable/not very repeatable.<br />
47
WJEC GCSE Additional Science Teacher’s Notes<br />
Discussion po<strong>in</strong>t<br />
On <strong>the</strong> basis of <strong>the</strong> evidence, do you th<strong>in</strong>k <strong>the</strong>re is a case for add<strong>in</strong>g calcium <strong>and</strong> magnesium salts <strong>to</strong><br />
dr<strong>in</strong>k<strong>in</strong>g water <strong>in</strong> soft water areas<br />
<br />
<br />
<br />
<br />
There appears <strong>to</strong> be no evidence for a specific l<strong>in</strong>k between calcium salts <strong>in</strong> water <strong>and</strong> heart<br />
benefits.<br />
There is some evidence that magnesium salts (>10mg/l) have a protective effect.<br />
No <strong>in</strong>formation is presented on any possible side-effects of <strong>the</strong>se salts.<br />
No evidence is presented on <strong>the</strong> effect of magnesium salts at <strong>the</strong> level suggested on <strong>the</strong> taste<br />
of water.<br />
48
WJEC GCSE Additional Science Teacher’s Notes<br />
14<br />
Simple electrical circuits<br />
_ Simple electrical circuits (pages 153–61)__________<br />
PRACTICAL Measur<strong>in</strong>g currents <strong>in</strong> series <strong>and</strong> parallel<br />
circuits (page 154)<br />
Students set up series <strong>and</strong> parallel circuits <strong>to</strong> determ<strong>in</strong>e that current is <strong>the</strong> same all <strong>the</strong> way<br />
around a series circuit, <strong>and</strong> that when current splits at a junction <strong>in</strong> a parallel circuit, <strong>the</strong> sum of<br />
<strong>the</strong> currents go<strong>in</strong>g <strong>in</strong><strong>to</strong> <strong>the</strong> junction equals <strong>the</strong> sum of <strong>the</strong> current com<strong>in</strong>g out of <strong>the</strong> junction.<br />
This is best shown with bulbs of different powers.<br />
Questions<br />
1. Study <strong>the</strong> follow<strong>in</strong>g circuits. Use your knowledge of <strong>the</strong> behaviour of current <strong>in</strong> series <strong>and</strong> parallel<br />
circuits <strong>to</strong> calculate <strong>the</strong> current at each of <strong>the</strong> marked po<strong>in</strong>ts on <strong>the</strong> circuit diagrams (a <strong>to</strong> j <strong>in</strong> Figure<br />
14.6).<br />
a 0.4 A d 0.2 A g 0.3 A j 1.2 A<br />
b 0.4 A e 0.6 A h 1.2 A<br />
c 0.4 A f 1.5 A i 0.3 A<br />
2. In a domestic house, all <strong>the</strong> electrical sockets, <strong>and</strong> all <strong>the</strong> domestic appliances such as an electric oven,<br />
are connected <strong>in</strong> parallel <strong>to</strong> <strong>the</strong> ma<strong>in</strong> circuit board. In one such house dur<strong>in</strong>g <strong>the</strong> early even<strong>in</strong>g, <strong>the</strong><br />
lights are us<strong>in</strong>g 2.5 A, a television 0.5 A, an electric oven 13 A <strong>and</strong> a kettle 10 A. What is <strong>the</strong> <strong>to</strong>tal<br />
current drawn from <strong>the</strong> ma<strong>in</strong> circuit board<br />
Total current = 2.5 + 0.5 + 13 + 10 = 26 A<br />
3. Draw circuits show<strong>in</strong>g <strong>the</strong> follow<strong>in</strong>g:<br />
a Two bulbs <strong>and</strong> a switch <strong>in</strong> series with a b A solar cell connected <strong>in</strong> parallel with two filament<br />
6 V power supply unit. lamps, each one with its own switch <strong>in</strong> series.<br />
49
WJEC GCSE Additional Science Teacher’s Notes<br />
PRACTICAL Measur<strong>in</strong>g voltages <strong>in</strong> series <strong>and</strong> parallel<br />
circuits (page 156)<br />
Students set up series <strong>and</strong> parallel circuits <strong>to</strong> determ<strong>in</strong>e that <strong>the</strong> sum of <strong>the</strong> voltages <strong>in</strong><strong>to</strong> a series<br />
circuit is <strong>the</strong> same as <strong>the</strong> sum of <strong>the</strong> voltages go<strong>in</strong>g out of <strong>the</strong> series circuit (with<strong>in</strong> experimental<br />
uncerta<strong>in</strong>ty) <strong>and</strong> that <strong>in</strong> parallel circuits, <strong>the</strong> voltage is <strong>the</strong> same across all components <strong>in</strong><br />
parallel.<br />
Discussion po<strong>in</strong>ts<br />
1. How are <strong>the</strong> lights <strong>in</strong> your kitchen (or lounge) at home connected Can you draw a circuit diagram<br />
show<strong>in</strong>g how <strong>the</strong>y (<strong>and</strong> <strong>the</strong>ir switches) are connected <strong>to</strong> your ma<strong>in</strong>s fuse board Do all <strong>the</strong> lights have<br />
<strong>the</strong> same operat<strong>in</strong>g voltage <strong>and</strong> power (measured <strong>in</strong> watts) Domestic electricity circuits are usually<br />
connected <strong>in</strong> a ‘r<strong>in</strong>g ma<strong>in</strong>’. F<strong>in</strong>d out what this means <strong>and</strong> why domestic circuits are connected this way.<br />
Domestic circuits are nearly always wired <strong>in</strong> parallel <strong>to</strong> <strong>the</strong> consumer unit. Each circuit with its<br />
own circuit breaker, <strong>and</strong> <strong>the</strong> whole supply fitted with a ma<strong>in</strong> circuit breaker wired <strong>in</strong> series<br />
with <strong>the</strong> consumer unit. There are a whole variety of ma<strong>in</strong>s light fitt<strong>in</strong>gs – <strong>the</strong>y usually have<br />
<strong>the</strong> same ma<strong>in</strong>s voltage, but different powers. An example of a r<strong>in</strong>g ma<strong>in</strong> is shown below.<br />
Domestic circuits are connected this way for safety reasons – this circuit m<strong>in</strong>imises accidents<br />
through short circuits.<br />
50
WJEC GCSE Additional Science Teacher’s Notes<br />
2. Be<strong>in</strong>g an electrician or an electrical eng<strong>in</strong>eer is a really good job. You can work for yourself or for a<br />
company. There are a great many opportunities at many different academic levels. Use <strong>the</strong> follow<strong>in</strong>g<br />
l<strong>in</strong>ks <strong>to</strong> f<strong>in</strong>d out more about careers <strong>in</strong>volv<strong>in</strong>g electricity:<br />
www.careerswales.com www.connexions-direct.com<br />
Investigate us<strong>in</strong>g <strong>the</strong> l<strong>in</strong>ks above <strong>and</strong> also www.futuremorph.org<br />
Questions<br />
4. A 12 V solar panel is used <strong>to</strong> run three household bulbs as shown <strong>in</strong> Figure 14.10.<br />
a Bethany connected a voltmeter across <strong>the</strong> solar cell. What voltage would she measure dur<strong>in</strong>g <strong>the</strong><br />
day<br />
12 V<br />
b Expla<strong>in</strong> why her voltmeter would read 0 V at midnight.<br />
No sunlight, so no generation of electricity.<br />
c<br />
Dur<strong>in</strong>g <strong>the</strong> day, Bethany connected <strong>the</strong> voltmeter across po<strong>in</strong>ts A <strong>and</strong> B <strong>in</strong> <strong>the</strong> circuit <strong>and</strong> turned on<br />
switch 1. What would her voltmeter read<br />
12 V<br />
d Expla<strong>in</strong> why <strong>the</strong> light<strong>in</strong>g circuit has three switches. What does each switch do<br />
Switch 1 controls <strong>the</strong> whole circuit, switch<strong>in</strong>g it on <strong>and</strong> off, Switch 2 controls bulb 1 <strong>and</strong><br />
Switch 3 controls bulb 2 <strong>and</strong> bulb 3.<br />
e Give an example (from your house) of a circuit like this where two bulbs work off <strong>the</strong> same switch.<br />
For example, wall lights <strong>in</strong> a lounge.<br />
f<br />
What is <strong>the</strong> advantage of connect<strong>in</strong>g bulb 1 with one switch compared <strong>to</strong> bulbs 2 <strong>and</strong> 3 which have<br />
one switch between <strong>the</strong>m<br />
Bulb 1 can be controlled <strong>in</strong>dependently – bulbs 2 <strong>and</strong> 3 are controlled <strong>to</strong>ge<strong>the</strong>r – <strong>the</strong>y are<br />
ei<strong>the</strong>r both ON or both OFF.<br />
g If bulb 2 <strong>and</strong> bulb 3 are exactly <strong>the</strong> same (same power rat<strong>in</strong>g <strong>and</strong> brightness), what voltage would<br />
Bethany measure if she closed all <strong>the</strong> switches <strong>and</strong> connected her voltmeter across po<strong>in</strong>ts A <strong>and</strong> C<br />
<strong>in</strong> <strong>the</strong> circuit<br />
6 V<br />
h Why would <strong>the</strong> voltage rat<strong>in</strong>g of bulb 1 be different from <strong>the</strong> voltage rat<strong>in</strong>gs of bulbs 2 <strong>and</strong> 3<br />
Bulb 1 has 12 V connected across it, whereas bulbs 2 <strong>and</strong> 3 only have 6 V across <strong>the</strong>m.<br />
5. Measur<strong>in</strong>g voltages <strong>in</strong> simple circuits <strong>in</strong> school is quite safe.<br />
a Why do electricians have <strong>to</strong> be much more careful when <strong>the</strong>y are measur<strong>in</strong>g voltages across<br />
components <strong>in</strong> a household wir<strong>in</strong>g circuit<br />
The voltages <strong>and</strong> <strong>the</strong> currents are usually much higher so <strong>the</strong> risk of electrocution is higher.<br />
b What precautions do you th<strong>in</strong>k that <strong>the</strong>y can take <strong>to</strong> m<strong>in</strong>imise <strong>the</strong> risks <strong>to</strong> <strong>the</strong>mselves<br />
Good tra<strong>in</strong><strong>in</strong>g, turn<strong>in</strong>g off <strong>the</strong> ma<strong>in</strong>s when work<strong>in</strong>g on any circuit, ensur<strong>in</strong>g all earth<br />
connections are connected, mak<strong>in</strong>g sure <strong>the</strong> circuit breakers/fuses are work<strong>in</strong>g.<br />
51
WJEC GCSE Additional Science Teacher’s Notes<br />
c<br />
Why is it always a good idea <strong>to</strong> ask an electrician <strong>to</strong> do electrical work on your house, if you don’t<br />
really know what you are do<strong>in</strong>g<br />
Electricians are tra<strong>in</strong>ed <strong>to</strong> do ma<strong>in</strong>s electrical work safely.<br />
6. Copy <strong>and</strong> complete Table 14.1 convert<strong>in</strong>g ohms <strong>to</strong> kilohms <strong>to</strong> megohms.<br />
Remember:<br />
1 MΩ = 1 000 000 Ω = 1000 kΩ<br />
1 kΩ = 0.001 MΩ = 1000 Ω<br />
1 Ω = 0.001 kΩ = 0.000 001 MΩ<br />
Resistance <strong>in</strong> ohms, Ω Resistance <strong>in</strong> kilohms, kΩ Resistance <strong>in</strong> megohms, MΩ<br />
1 000 000 1 000 1<br />
4 000 4 0.004<br />
2 0.002 0.000 002<br />
3 000 3 0.003<br />
220 000 220 0.220<br />
6 000 000 6 000 6<br />
10 000 10 0.010<br />
PRACTICAL Measur<strong>in</strong>g current <strong>and</strong> voltage <strong>in</strong> circuits<br />
controlled by a variable resis<strong>to</strong>r (page 159)<br />
1. Graphs of voltage aga<strong>in</strong>st current for components are called ‘electrical characteristics’. Plot electrical<br />
characteristic graphs for <strong>the</strong> fixed resis<strong>to</strong>r <strong>and</strong> <strong>the</strong> bulb. If you can, plot <strong>the</strong>m both on <strong>the</strong> same graph<br />
us<strong>in</strong>g <strong>the</strong> same axes.<br />
Student graphs should resemble <strong>the</strong> one below. The red l<strong>in</strong>e is for <strong>the</strong> fixed resis<strong>to</strong>r, <strong>the</strong> blue<br />
l<strong>in</strong>e for <strong>the</strong> bulb.<br />
52
WJEC GCSE Additional Science Teacher’s Notes<br />
2. Describe <strong>in</strong> words <strong>the</strong> pattern of each graph. This means that you have <strong>to</strong> describe how <strong>the</strong> voltage<br />
(on <strong>the</strong> y-axis) varies with <strong>the</strong> current (on <strong>the</strong> x-axis).<br />
Resis<strong>to</strong>r – voltage is proportional <strong>to</strong> current (graph is l<strong>in</strong>ear with a positive gradient).<br />
Bulb – voltage <strong>in</strong>creases faster than current (graph is curved with <strong>in</strong>creas<strong>in</strong>g positive<br />
gradient).<br />
3. Expla<strong>in</strong> how a variable resis<strong>to</strong>r can be used <strong>in</strong> a circuit <strong>to</strong> control <strong>the</strong> current through <strong>and</strong> <strong>the</strong> voltage<br />
across o<strong>the</strong>r components.<br />
Alter<strong>in</strong>g <strong>the</strong> resistance of a circuit alters <strong>the</strong> current flow<strong>in</strong>g through <strong>the</strong> circuit. If <strong>the</strong><br />
current is altered <strong>the</strong>n <strong>the</strong> voltage across <strong>the</strong> o<strong>the</strong>r components will change due <strong>to</strong> Ohm’s<br />
law.<br />
Questions<br />
7. Us<strong>in</strong>g <strong>the</strong> data that you collected for <strong>the</strong> Practical: Measur<strong>in</strong>g current <strong>and</strong> voltage <strong>in</strong> circuits<br />
controlled by a variable resis<strong>to</strong>r, construct two tables. One table will be for <strong>the</strong> fixed resis<strong>to</strong>r data,<br />
<strong>and</strong> <strong>the</strong> o<strong>the</strong>r table will be for <strong>the</strong> bulb.<br />
The values <strong>in</strong> <strong>the</strong> table will depend on <strong>the</strong> students’ results from <strong>the</strong> Practical.<br />
8. Describe <strong>the</strong> patterns <strong>in</strong> your results for Question 7. How does <strong>the</strong> resistance of <strong>the</strong> fixed resis<strong>to</strong>r vary<br />
with current (or voltage) How does <strong>the</strong> resistance of <strong>the</strong> bulb vary with current (or voltage)<br />
The resistance of <strong>the</strong> fixed resis<strong>to</strong>r is constant for different values of current (or voltage).<br />
The resistance of <strong>the</strong> bulb will <strong>in</strong>crease with an <strong>in</strong>creas<strong>in</strong>g current (or voltage).<br />
9. A 25 Ω fixed resis<strong>to</strong>r has a current of 2 A through it. Calculate <strong>the</strong> voltage across <strong>the</strong> fixed resis<strong>to</strong>r.<br />
V = I × R; V = 2 × 25 = 50 V<br />
10. In a mobile phone circuit, 1.5 V is applied across a keyboard circuit with a resistance of 5000 Ω. What is<br />
<strong>the</strong> current <strong>in</strong> <strong>the</strong> keyboard circuit<br />
V<br />
I R<br />
V<br />
so I <br />
R<br />
1.5<br />
5000<br />
0.003 A<br />
11. Figure 14.13 shows <strong>the</strong> electrical characteristic of a 12 V car bulb. Use <strong>the</strong> graph <strong>to</strong> calculate <strong>the</strong><br />
resistance of <strong>the</strong> bulb when <strong>the</strong> current through <strong>the</strong> bulb is:<br />
a 0.2 A V = 0.4 V so R =<br />
b 0.6 A V = 3.6 V so R =<br />
c 1.0 A V = 10.0 V so R =<br />
0.4<br />
= 2 <br />
0.2<br />
3.6<br />
= 6 <br />
0.6<br />
10 .0 = 10 <br />
1.0<br />
12. Expla<strong>in</strong> why <strong>the</strong> resistance of a bulb changes when more current is passed through it. (H<strong>in</strong>t: when <strong>the</strong><br />
bulb has more current go<strong>in</strong>g through it, it is brighter <strong>and</strong> hotter. How might this affect <strong>the</strong> structure of<br />
<strong>the</strong> metal filament)<br />
As more current flows through <strong>the</strong> filament, <strong>the</strong>re will be more collisions of <strong>the</strong> free electrons<br />
with <strong>the</strong> structure of <strong>the</strong> metal filament <strong>and</strong> <strong>the</strong> electrons <strong>the</strong>mselves. This heats <strong>the</strong> filament<br />
53
WJEC GCSE Additional Science Teacher’s Notes<br />
caus<strong>in</strong>g <strong>the</strong> positive ion cores of <strong>the</strong> filament <strong>to</strong> vibrate more, caus<strong>in</strong>g even more collisions<br />
with <strong>the</strong> free electrons, <strong>in</strong>creas<strong>in</strong>g <strong>the</strong> resistance of <strong>the</strong> filament.<br />
13. A rheostat (large variable resis<strong>to</strong>r) is set up with a resistance of 12 Ω. A 0–12 V variable power supply<br />
is connected <strong>in</strong> series with an ammeter <strong>and</strong> <strong>the</strong> rheostat.<br />
a Draw a circuit diagram of this arrangement.<br />
b Use <strong>the</strong> data supplied <strong>and</strong> Ohm’s law <strong>to</strong> determ<strong>in</strong>e <strong>the</strong> current through <strong>the</strong> rheostat, for voltages of<br />
0 V, 2 V, 4 V, 6 V, 8 V, 10 V <strong>and</strong> 12 V.<br />
V<br />
I <br />
R<br />
Voltage, V, (V) 0 2 4 6 8 10 12<br />
Current, I, (A) 0.00 0.17 0.33 0.50 0.67 0.83 1.00<br />
c<br />
Plot an electrical characteristic graph of <strong>the</strong> rheostat. Plot <strong>the</strong> voltage on <strong>the</strong> y-axis <strong>and</strong> <strong>the</strong> current<br />
on <strong>the</strong> x-axis. Draw a best-fit l<strong>in</strong>e through <strong>the</strong> po<strong>in</strong>ts <strong>and</strong> label this l<strong>in</strong>e ‘12 Ω’.<br />
d Calculate <strong>the</strong> gradient (slope) of <strong>the</strong> best-fit l<strong>in</strong>e. Compare this value <strong>to</strong> <strong>the</strong> resistance of <strong>the</strong><br />
rheostat.<br />
Gradient = 12 – <strong>the</strong> same as <strong>the</strong> resistance of <strong>the</strong> rheostat.<br />
e The resistance of <strong>the</strong> rheostat is now changed <strong>to</strong> 6 Ω. On <strong>the</strong> same electrical characteristic graph,<br />
sketch <strong>the</strong> graph for <strong>the</strong> new resistance sett<strong>in</strong>g <strong>and</strong> label this ‘6 Ω’. Expla<strong>in</strong> why you have drawn<br />
<strong>the</strong> sketch l<strong>in</strong>e where it is.<br />
The resistance is halved so <strong>the</strong> gradient will halve – <strong>the</strong> l<strong>in</strong>e will go through (1.0, 6).<br />
54
WJEC GCSE Additional Science Teacher’s Notes<br />
_ Electrical power (pages 162–63)_________________<br />
Questions<br />
14. Calculate <strong>the</strong> power of a 6 V <strong>to</strong>rch bulb draw<strong>in</strong>g a current of 0.8 A.<br />
P = V × I = 6 × 0.8 = 4.8 W<br />
15. A current of 5 A passes through a lamp with a resistance of 2.4 Ω, <strong>and</strong> <strong>the</strong>n through a small cool<strong>in</strong>g fan<br />
of resistance 4 Ω. Calculate <strong>the</strong> power of each component <strong>and</strong> hence calculate <strong>the</strong> <strong>to</strong>tal power drawn<br />
from <strong>the</strong> circuit.<br />
Lamp: P = I 2 × R = 5 2 × 2.4 = 60 W<br />
Fan: P = I 2 × R = 5 2 × 4 = 100 W<br />
Total power = 160 W<br />
16. Study <strong>the</strong> circuit diagram <strong>in</strong> Figure 14.14.<br />
a Calculate <strong>the</strong> power of each bulb.<br />
6 bulb: P = I 2 × R = 2.5 2 × 6 = 37.5 W<br />
12 bulb: P = I 2 × R = 2.5 2 × 12 = 75 W<br />
b Calculate <strong>the</strong> <strong>to</strong>tal power drawn from <strong>the</strong> power supply.<br />
Total power = 37.5 + 75 = 112.5 W<br />
c<br />
Calculate <strong>the</strong> voltage of <strong>the</strong> power supply.<br />
V<br />
P 112.5 45 V<br />
I 2.5<br />
d Calculate <strong>the</strong> voltage across each bulb.<br />
6 bulb: V = I × R = 2.5 × 6 = 15 V<br />
12 bulb: V = I × R = 2.5 × 12 = 30 V<br />
17. A ma<strong>in</strong>s hairdryer operates with a voltage of 220 V.<br />
a Calculate <strong>the</strong> power when it is on its HIGH sett<strong>in</strong>g, draw<strong>in</strong>g a current of 8 A.<br />
P = V × I = 220 × 8 = 1760 W<br />
b The LOW sett<strong>in</strong>g operates with a power of 1 kW (1000 W). Calculate <strong>the</strong> current flow<strong>in</strong>g through <strong>the</strong><br />
hairdryer.<br />
P 1000<br />
I 4.5 A<br />
V 220<br />
c<br />
The hairdryer can also be used <strong>in</strong> <strong>the</strong> United States where <strong>the</strong> ma<strong>in</strong>s voltage is different. The power<br />
given out by <strong>the</strong> hairdryer is <strong>the</strong> same as <strong>in</strong> <strong>the</strong> UK (your answer <strong>to</strong> part a), but <strong>the</strong> current flow<strong>in</strong>g<br />
through <strong>the</strong> hairdryer is 16 A. Calculate <strong>the</strong> voltage of <strong>the</strong> ma<strong>in</strong>s <strong>in</strong> <strong>the</strong> USA.<br />
P 1760<br />
V 110 V<br />
I 16<br />
55
WJEC GCSE Additional Science Teacher’s Notes<br />
15<br />
Distance, speed <strong>and</strong><br />
acceleration<br />
_ Measur<strong>in</strong>g speeds (pages 165–67)_______________<br />
TASK The animal olympics 100 m f<strong>in</strong>al (pages 166–67)<br />
1. Each animal f<strong>in</strong>ishes <strong>the</strong> 100 m race. Use <strong>the</strong> data <strong>to</strong> calculate <strong>the</strong> times for each competi<strong>to</strong>r.<br />
Animal<br />
Top speed Distance<br />
(m/s) travelled (m)<br />
Time (s)<br />
Cheetah 31 100 3.2<br />
Pronghorn antelope 27 100 3.7<br />
Lion 22 100 4.5<br />
Spr<strong>in</strong>gbok 22 100 4.5<br />
Horse 21 100 4.8<br />
Elk 20 100 5.0<br />
Coyote 19 100 5.3<br />
Usa<strong>in</strong> Bolt 19 100 5.3<br />
2. Expla<strong>in</strong> why, <strong>in</strong> reality, <strong>the</strong> times for each competi<strong>to</strong>r will be higher than those that you have<br />
calculated.<br />
The animals (<strong>and</strong> Usa<strong>in</strong> Bolt) do not run at <strong>to</strong>p speed for <strong>the</strong> whole race, <strong>the</strong>y start at 0 m/s<br />
<strong>and</strong> accelerate <strong>to</strong> <strong>to</strong>p speed.<br />
3. Usa<strong>in</strong> Bolt broke <strong>the</strong> World 100 m record <strong>in</strong> <strong>the</strong> Beij<strong>in</strong>g Olympic f<strong>in</strong>al <strong>in</strong> 2008, <strong>and</strong> this record<br />
break<strong>in</strong>g run has been one of <strong>the</strong> most closely analysed runs <strong>in</strong> his<strong>to</strong>ry, although he subsequently<br />
broke his own world record <strong>in</strong> <strong>the</strong> 2009 World Championships. Usa<strong>in</strong> Bolt’s mean times for <strong>the</strong> 2008<br />
f<strong>in</strong>al race were as shown <strong>in</strong> Table 15.2.<br />
a Make a copy of this table, but add a third column labelled ‘Average speed, m/s’. Calculate Usa<strong>in</strong><br />
Bolt’s mean speed for each 10 m segment of <strong>the</strong> race <strong>and</strong> fill <strong>in</strong> your table.<br />
Distance (m)<br />
Split time (s)<br />
Average speed <strong>in</strong><br />
segment (m/s)<br />
Reaction time <strong>to</strong> leave blocks 0.165 0.0<br />
0–10 (<strong>in</strong>clud<strong>in</strong>g reaction time) 1.85 5.4<br />
10–20 1.02 9.8<br />
20–30 0.91 11.0<br />
30–40 0.87 11.5<br />
40–50 0.85 11.8<br />
50–60 0.82 12.2<br />
60–70 0.82 12.2<br />
70–80 0.82 12.2<br />
80–90 0.83 12.0<br />
90–100 0.90 11.1<br />
0–100 9.69 10.3<br />
56
WJEC GCSE Additional Science Teacher’s Notes<br />
b Plot a graph of Usa<strong>in</strong> Bolt’s mean speed (on <strong>the</strong> y-axis) aga<strong>in</strong>st distance (on <strong>the</strong> x-axis). Take<br />
<strong>the</strong> mean speed <strong>to</strong> occur <strong>in</strong> <strong>the</strong> middle of each 10 m segment of <strong>the</strong> race, so plot <strong>the</strong> distances<br />
as: 5 m, 15 m, 25 m <strong>and</strong> so on up <strong>to</strong> 95 m.<br />
See graph under part (d) below.<br />
c<br />
Describe <strong>the</strong> pattern (or shape) of <strong>the</strong> graph <strong>and</strong> try <strong>to</strong> expla<strong>in</strong> how mean speed varies with<br />
distance.<br />
The average speed <strong>in</strong>creases from zero <strong>to</strong> about 10 m/s <strong>in</strong> a distance of 15 m – as Usa<strong>in</strong><br />
was accelerat<strong>in</strong>g out <strong>and</strong> away from <strong>the</strong> blocks. After 15 m, <strong>the</strong> average speed <strong>in</strong>creases<br />
more slowly up <strong>to</strong> a maximum of just over 12 m/s for about 70 m – when Usa<strong>in</strong> was<br />
runn<strong>in</strong>g at maximum speed. After this Usa<strong>in</strong> slowed back <strong>to</strong> about 11 m/s for <strong>the</strong> last 15<br />
m – as he was lung<strong>in</strong>g for <strong>the</strong> l<strong>in</strong>e.<br />
d In 2009, <strong>the</strong> C<strong>in</strong>c<strong>in</strong>nati Zoo’s 8-year-old female cheetah Sarah became <strong>the</strong> world’s fastest l<strong>and</strong><br />
mammal. Sarah covered 100 m <strong>in</strong> a time of 6.13 seconds, break<strong>in</strong>g <strong>the</strong> previous mark of 6.19<br />
seconds set by a male South African cheetah named Nyana <strong>in</strong> 2001. Use this <strong>in</strong>formation<br />
(assum<strong>in</strong>g that a cheetah will have a similar pattern of runn<strong>in</strong>g <strong>to</strong> Usa<strong>in</strong> Bolt) <strong>to</strong> sketch on <strong>the</strong><br />
same graph <strong>the</strong> pattern for Sarah compared with Usa<strong>in</strong> Bolt.<br />
Sarah <strong>the</strong> cheetah<br />
Usa<strong>in</strong> Bolt<br />
Discussion po<strong>in</strong>ts<br />
1. You can f<strong>in</strong>d lots of videos of Usa<strong>in</strong> Bolt’s 2008 Olympic 100 m f<strong>in</strong>al onl<strong>in</strong>e. Watch <strong>the</strong> race. It<br />
almost feels as if he is slow<strong>in</strong>g down at <strong>the</strong> end <strong>and</strong> wav<strong>in</strong>g <strong>to</strong> <strong>the</strong> crowd, yet <strong>in</strong> reality he’s still<br />
runn<strong>in</strong>g at <strong>to</strong>p speed. How much faster do you th<strong>in</strong>k human be<strong>in</strong>gs can run Is <strong>the</strong>re go<strong>in</strong>g <strong>to</strong> be an<br />
ultimate ‘<strong>to</strong>p speed’ or do you th<strong>in</strong>k that humans will get progressively quicker <strong>and</strong> quicker<br />
Many suitable l<strong>in</strong>ks are available on youtube.com. Some <strong>in</strong>terest<strong>in</strong>g views on how fast a<br />
human be<strong>in</strong>g can run are available from Peter Wey<strong>and</strong> from Sou<strong>the</strong>rn Methodist University,<br />
USA:<br />
http://smu.edu/education/APW/Locomo<strong>to</strong>rNews.asp<br />
2. The cheetah has a substantially faster <strong>to</strong>p speed than most of its prey (for example <strong>the</strong> spr<strong>in</strong>gbok),<br />
yet it only has a 50% kill success rate. Why do you th<strong>in</strong>k that half of <strong>the</strong> cheetah’s prey get away<br />
Cheetahs can reach a speed approach<strong>in</strong>g 70 mph (110 km/h), however this speed can be<br />
ma<strong>in</strong>ta<strong>in</strong>ed for only a few hundred metres or for about one m<strong>in</strong>ute. If it is forced <strong>to</strong> run<br />
longer than a m<strong>in</strong>ute, it usually gives up <strong>the</strong> chase.<br />
57
WJEC GCSE Additional Science Teacher’s Notes<br />
_ Speed or velocity (page 168)___________________<br />
Discussion po<strong>in</strong>ts<br />
Many D of E expeditions <strong>in</strong>volve multiple routes <strong>in</strong> many directions. Why is it important that D of E<br />
assessors <strong>and</strong> group leaders know <strong>the</strong> average walk<strong>in</strong>g speed of a group over given terra<strong>in</strong>s, <strong>and</strong> must<br />
ensure that all group members can read a compass correctly<br />
By know<strong>in</strong>g <strong>the</strong> average walk<strong>in</strong>g speed of a group, <strong>the</strong> assessor knows <strong>the</strong> average distance that<br />
<strong>the</strong> group can travel <strong>in</strong> a given time. If <strong>the</strong> group can read a compass, <strong>the</strong>n <strong>the</strong> assessor can judge<br />
when <strong>to</strong> meet <strong>the</strong>m at pre-determ<strong>in</strong>ed checkpo<strong>in</strong>ts.<br />
_Acceleration: speed<strong>in</strong>g up <strong>and</strong> slow<strong>in</strong>g down________<br />
(pages 168–70)<br />
Questions<br />
1. Table 15.3 shows some data for some of <strong>the</strong> world’s fastest production cars, <strong>and</strong> for comparison, a<br />
st<strong>and</strong>ard Ford Focus 1.8. Copy <strong>and</strong> complete <strong>the</strong> table (without <strong>the</strong> pictures) by calculat<strong>in</strong>g <strong>the</strong><br />
acceleration of each car.<br />
Car<br />
Time (s) <strong>to</strong> reach 100 km/h<br />
(27.7 m/s) from a st<strong>and</strong><strong>in</strong>g start<br />
Acceleration (m/s 2 )<br />
Bugatti Veyron Super Sport 2.4 11.5<br />
Ariel A<strong>to</strong>m V8 2.5 11.1<br />
Porsche 911 Turbo S 2.7 10.3<br />
Nissan GT-R 2.8 9.9<br />
Maclaren MP4-12C 3.1 8.9<br />
Ford Focus 1.8 10.3 2.7<br />
2. Travell<strong>in</strong>g on a mo<strong>to</strong>rway, HGV lorries are usually speed limited <strong>to</strong> 60 mph or 27 m/s. A Ford Focus 1.8<br />
travell<strong>in</strong>g beh<strong>in</strong>d an HGV lorry travell<strong>in</strong>g at 27 m/s accelerates <strong>to</strong> 70 mph or 31 m/s <strong>in</strong> 2 seconds, <strong>in</strong><br />
order <strong>to</strong> overtake <strong>the</strong> HGV lorry. What is <strong>the</strong> acceleration of <strong>the</strong> Ford Focus How does this compare<br />
with its maximum acceleration<br />
acceleration<br />
<br />
change <strong>in</strong> velocity<br />
time<br />
<br />
31- 27<br />
2<br />
4<br />
2 m/s<br />
2<br />
_Graphs of motion (pages 170–72)________________<br />
Questions<br />
3. Describe <strong>the</strong> motion of <strong>the</strong> objects illustrated by <strong>the</strong> distance–time graphs (a), (b) <strong>and</strong> (c) <strong>in</strong> Figure 15.6.<br />
a Object mov<strong>in</strong>g at a constant speed for 5 s.<br />
b Object stationary 20 m away from an orig<strong>in</strong> for 5 s.<br />
c Object mov<strong>in</strong>g at a constant speed for 20 s, <strong>the</strong>n at a slower constant speed for 20s.<br />
4. Calculate <strong>the</strong> mean velocity of <strong>the</strong> object mov<strong>in</strong>g <strong>in</strong> (a).<br />
6 m/s<br />
5. Calculate <strong>the</strong> two mean velocities illustrated by distance−time graph (c).<br />
10 m/s <strong>the</strong>n 5 m/s<br />
58
WJEC GCSE Additional Science Teacher’s Notes<br />
6. Sketch distance−time graphs for <strong>the</strong> follow<strong>in</strong>g:<br />
a An object mov<strong>in</strong>g 20 m <strong>in</strong> 4 s, <strong>the</strong>n stationary for 3 s, <strong>the</strong>n mov<strong>in</strong>g back <strong>to</strong> <strong>the</strong> start <strong>in</strong> 8 s.<br />
25<br />
20<br />
distance (m)<br />
15<br />
10<br />
5<br />
0<br />
0 2 4 6 8 10 12 14 16<br />
time (s)<br />
b An object stationary for 2 s <strong>the</strong>n mov<strong>in</strong>g at a constant velocity of 5 m/s for 10 s, <strong>the</strong>n stationary for<br />
ano<strong>the</strong>r 2 s.<br />
60<br />
50<br />
distance (m)<br />
40<br />
30<br />
20<br />
10<br />
0<br />
0 2 4 6 8 10 12 14 16<br />
time (s)<br />
c<br />
An object mov<strong>in</strong>g 10 m <strong>in</strong> 5 s, <strong>the</strong>n mov<strong>in</strong>g <strong>in</strong> <strong>the</strong> same direction at a constant velocity of 4 m/s for<br />
3 s, <strong>the</strong>n mov<strong>in</strong>g back <strong>to</strong> <strong>the</strong> start <strong>in</strong> 4 s.<br />
25<br />
20<br />
distance (m)<br />
15<br />
10<br />
5<br />
0<br />
0 2 4 6 8 10 12 14<br />
time (s)<br />
59
WJEC GCSE Additional Science Teacher’s Notes<br />
PRACTICAL Measur<strong>in</strong>g, plott<strong>in</strong>g <strong>and</strong> analys<strong>in</strong>g real<br />
distance–time graphs (pages 171–72)<br />
A student will need <strong>to</strong> be primed <strong>to</strong> br<strong>in</strong>g <strong>in</strong> a bicycle (with helmet) before-h<strong>and</strong>. This practical<br />
task requires quite a lot of organisation – a schematic diagram of who is do<strong>in</strong>g what <strong>and</strong><br />
st<strong>and</strong><strong>in</strong>g where will help considerably – go through this <strong>in</strong> <strong>the</strong> labora<strong>to</strong>ry before go<strong>in</strong>g outside.<br />
A suitable data record<strong>in</strong>g sheet could look like:<br />
Motion<br />
Walk<strong>in</strong>g<br />
Runn<strong>in</strong>g<br />
Cycl<strong>in</strong>g<br />
Time <strong>to</strong><br />
reach 5 m<br />
cone (s)<br />
Time <strong>to</strong><br />
reach 10 m<br />
cone (s)<br />
Time <strong>to</strong><br />
reach 15 m<br />
cone (s)<br />
Time <strong>to</strong><br />
reach 20 m<br />
cone (s)<br />
Time <strong>to</strong><br />
reach 25 m<br />
cone (s)<br />
Time <strong>to</strong><br />
reach 30 m<br />
cone (s)<br />
1 2 3 Av 1 2 3 Av 1 2 3 Av 1 2 3 Av 1 2 3 Av 1 2 3 Av<br />
Answers <strong>to</strong> <strong>the</strong> ‘Analys<strong>in</strong>g your results’ <strong>questions</strong> will depend on <strong>the</strong> results ga<strong>the</strong>red.<br />
_ Velocity–time graphs (pages 172–74)____________<br />
Question<br />
7. Describe <strong>the</strong> motion of <strong>the</strong> objects illustrated by <strong>the</strong> velocity–time graphs <strong>in</strong> Figure 15.8. For each graph<br />
calculate any accelerations/decelerations <strong>and</strong> (HT only) <strong>the</strong> <strong>to</strong>tal distance travelled.<br />
a (Top left) Object stationary for 2 s <strong>the</strong>n accelerat<strong>in</strong>g at 3 m/s 2 for 2 s, reach<strong>in</strong>g<br />
maximum velocity of 6 m/s, <strong>the</strong>n travell<strong>in</strong>g at constant 6 m/s <strong>in</strong> same direction<br />
for 6 s<br />
b (Middle left) Object accelerat<strong>in</strong>g at 3 m/s 2 for 3 s, reach<strong>in</strong>g velocity of 9 m/s, <strong>the</strong>n<br />
travell<strong>in</strong>g at a constant 9 m/s <strong>in</strong> <strong>the</strong> same direction for 4 s before decelerat<strong>in</strong>g<br />
(<strong>in</strong> <strong>the</strong> same direction) at 3 m/s 2 (or accelerat<strong>in</strong>g at –3m/s 2 ) for 3 s before<br />
com<strong>in</strong>g <strong>to</strong> rest at t = 10 s<br />
c (Bot<strong>to</strong>m left) Object accelerat<strong>in</strong>g at 4 m/s 2 for 2 s, reach<strong>in</strong>g velocity of 8 m/s, <strong>the</strong>n<br />
decelerat<strong>in</strong>g (<strong>in</strong> <strong>the</strong> same direction) at 2 m/s 2 (or accelerat<strong>in</strong>g at –2m/s 2 ) for<br />
4 s before accelerat<strong>in</strong>g aga<strong>in</strong> at 3m/s 2 <strong>in</strong> <strong>the</strong> same direction for 3 s reach<strong>in</strong>g a<br />
velocity of 9 m/s before decelerat<strong>in</strong>g (<strong>in</strong> <strong>the</strong> same direction) at 9 m/s 2 before<br />
com<strong>in</strong>g <strong>to</strong> rest at t = 10 s<br />
d (Top right) Object <strong>in</strong>itially travell<strong>in</strong>g at 9 m/s, decelerat<strong>in</strong>g at 3 m/s 2 for 3 s, com<strong>in</strong>g <strong>to</strong><br />
rest at t = 3 s, <strong>the</strong>n accelerat<strong>in</strong>g (<strong>in</strong> <strong>the</strong> same direction) at 2 m/s 2 for 4 s<br />
reach<strong>in</strong>g a velocity of 8 m/s <strong>and</strong> <strong>the</strong>n travell<strong>in</strong>g at this constant velocity for 3 s<br />
e (Top right) Object travell<strong>in</strong>g at a constant velocity of 6 m/s for 3 s <strong>the</strong>n accelerat<strong>in</strong>g at 2<br />
m/s 2 for 1 s, reach<strong>in</strong>g velocity of 8 m/s <strong>and</strong> stay<strong>in</strong>g at this constant velocity of<br />
8 m/s for 1 s before decelerat<strong>in</strong>g (<strong>in</strong> <strong>the</strong> same direction) at 2 m/s 2 (or<br />
accelerat<strong>in</strong>g at –2m/s 2 ) for 4 s before com<strong>in</strong>g <strong>to</strong> rest at t = 9 s<br />
60
WJEC GCSE Additional Science Teacher’s Notes<br />
16<br />
The effect of forces<br />
_ Mov<strong>in</strong>g <strong>in</strong> space (pages 176–78)_________________<br />
Discussion po<strong>in</strong>t<br />
What would it be like <strong>to</strong> live for 180 days on <strong>the</strong> ISS (a typical mission duration) What sort of th<strong>in</strong>gs <strong>in</strong> your<br />
daily rout<strong>in</strong>e would be difficult on <strong>the</strong> ISS <strong>in</strong> low Earth orbit<br />
Many websites chronicle <strong>the</strong> daily life of astronauts <strong>and</strong> cosmonauts on-board <strong>the</strong> ISS. Examples<br />
<strong>in</strong>clude:<br />
www.science<strong>in</strong>school.org/2008/issue10/iss<br />
www.nasa.gov/audience/foreduca<strong>to</strong>rs/teach<strong>in</strong>gfromspace/day<strong>in</strong><strong>the</strong>life/<strong>in</strong>dex.html<br />
PRACTICAL Analys<strong>in</strong>g <strong>the</strong> gravitational field strength of<br />
<strong>the</strong> Earth (page 177)<br />
This is a straight-forward activity that could be extended by giv<strong>in</strong>g students a range of different<br />
balances <strong>and</strong> new<strong>to</strong>n meters.<br />
weight <strong>in</strong> N <br />
1. For each slotted mass comb<strong>in</strong>ation, calculate <strong>the</strong> sum g<br />
<br />
, <strong>and</strong> record this <strong>in</strong> <strong>the</strong><br />
mass <strong>in</strong> kg <br />
last column of <strong>the</strong> table.<br />
Values should be approximately 10 N/kg<br />
2. Look at <strong>the</strong> values of g that you have calculated – is <strong>the</strong>re a pattern<br />
The values should all be approximately <strong>the</strong> same (~10 N/kg).<br />
3. Calculate <strong>the</strong> average value of g.<br />
Value depends upon values recorded by students (~10 N/kg).<br />
4. Use <strong>the</strong> range of <strong>the</strong> values <strong>to</strong> state an uncerta<strong>in</strong>ty on your value of g, i.e. g = (average value ±<br />
uncerta<strong>in</strong>ty) N/kg.<br />
A reasonable way <strong>to</strong> calculate <strong>the</strong> uncerta<strong>in</strong>ty is ±(range/2).<br />
5. Plot a graph of weight (N) on <strong>the</strong> y-axis aga<strong>in</strong>st mass (kg) on <strong>the</strong> x-axis.<br />
Student graph<br />
6. Draw a best-fit straight l<strong>in</strong>e through your po<strong>in</strong>ts (make sure your l<strong>in</strong>e goes through <strong>the</strong> orig<strong>in</strong>).<br />
Best-fit l<strong>in</strong>e<br />
7. Calculate <strong>the</strong> gradient (slope) of your best-fit l<strong>in</strong>e. Compare your value with <strong>the</strong> average value of g<br />
that you calculated earlier. The gradient of this l<strong>in</strong>e is <strong>the</strong> value of g.<br />
gradient vertical displacement<br />
horizontal displacement<br />
≈ 10 N/kg Values should be very similar.<br />
61
WJEC GCSE Additional Science Teacher’s Notes<br />
8. The value of g is approximately 10 N/kg. How close <strong>to</strong> this value is:<br />
a your average calculated value<br />
b <strong>the</strong> gradient of your graph<br />
Calculated deviations from 10 N/kg should be very small.<br />
9. How could you use your graph <strong>to</strong> determ<strong>in</strong>e a value of <strong>the</strong> uncerta<strong>in</strong>ty of <strong>the</strong> value of g<br />
Plot range bars <strong>and</strong> get a range of different ‘best-fit’ l<strong>in</strong>es (maximum/m<strong>in</strong>imum/best-fit).<br />
10. Why is it more accurate <strong>to</strong> measure <strong>the</strong> weight of a slotted mass with a New<strong>to</strong>n meter with <strong>the</strong><br />
lowest range capable of measur<strong>in</strong>g it<br />
Lower ranges will have greater precision.<br />
11. Would it be better <strong>to</strong> measure all <strong>the</strong> weights with <strong>the</strong> same (bigger ranged) New<strong>to</strong>n meter<br />
This leads <strong>to</strong> an <strong>in</strong>terest<strong>in</strong>g discussion of precision v zero-<strong>in</strong>g errors. Answer: depends on<br />
<strong>the</strong> quality of <strong>the</strong> New<strong>to</strong>n meter.<br />
Discussion po<strong>in</strong>t<br />
When we are liv<strong>in</strong>g <strong>in</strong> <strong>the</strong> Earth’s gravitational field we live <strong>in</strong> a world of 1 g, that is, 1 × <strong>the</strong> Earth’s<br />
gravitational field. At take-off, <strong>the</strong> astronauts experience 3 g (3 × <strong>the</strong> Earth’s gravitational field strength). In<br />
orbit, <strong>the</strong> astronauts effectively experience 0 g. What do you th<strong>in</strong>k <strong>the</strong>se gravitational fields ‘feel’ like<br />
There is an <strong>in</strong>terest<strong>in</strong>g <strong>in</strong>terview with Dr Mae Jemison (STS-47 Shuttle Endeavour 1992):<br />
http://teacher.scholastic.com/space/mae_jemison/<strong>in</strong>terview.htm<br />
Questions<br />
1. A typical ISS module has a mass of 22 700 kg. Each of <strong>the</strong> two Space Shuttle solid rocket boosters has<br />
a lift-off mass of 590 000 kg, <strong>and</strong> <strong>the</strong> external fuel tank (filled with rocket fuel) has a lift-off mass of 760<br />
000 kg.<br />
a Calculate <strong>the</strong> weight of each component of <strong>the</strong> Space Shuttle launch system.<br />
Space Shuttle: mass = 78 000 kg weight = 780 000 N<br />
ISS Module: mass = 22 700 kg weight = 227 000 N<br />
Solid rocket booster: mass = 590 000 kg weight = 5 900 000 N (×2 = 11 800 000 N)<br />
External fuel tank: mass = 760 000 kg weight = 7 600 000 N<br />
b What is <strong>the</strong> <strong>to</strong>tal lift-off weight of <strong>the</strong> Space Shuttle launch system<br />
Total weight at take off = 20 407 000 N<br />
c<br />
What is <strong>the</strong> m<strong>in</strong>imum <strong>to</strong>tal thrust needed by <strong>the</strong> Space Shuttle ma<strong>in</strong> eng<strong>in</strong>es <strong>and</strong> <strong>the</strong> solid fuel<br />
rocket boosters Why is this a ‘m<strong>in</strong>imum’<br />
M<strong>in</strong>imum thrust = <strong>to</strong>tal weight = 20 407 000 N<br />
The <strong>to</strong>tal thrust of <strong>the</strong> eng<strong>in</strong>es does not act directly downwards – some of <strong>the</strong> thrust acts at<br />
an angle <strong>to</strong> <strong>the</strong> vertical as <strong>the</strong> combustion products come out of <strong>the</strong> jet eng<strong>in</strong>es.<br />
2. The last Space Shuttle launch <strong>to</strong>ok place <strong>in</strong> June 2011. From that po<strong>in</strong>t on, <strong>the</strong> ISS will be serviced via<br />
Russian Progress <strong>and</strong> American Dragon spacecraft whilst astronauts will travel <strong>to</strong> <strong>and</strong> from <strong>the</strong> ISS <strong>in</strong><br />
Russian Soyuz spacecraft. All Russian spacecraft are launched via Soyuz-2 rockets <strong>and</strong> <strong>the</strong> American<br />
spacecraft will be launched with Falcon 9 rockets (Table 16.2). Copy <strong>and</strong> complete <strong>the</strong> table,<br />
calculat<strong>in</strong>g <strong>the</strong> launch weight of each rocket <strong>and</strong> <strong>the</strong> m<strong>in</strong>imum resultant upwards force at launch.<br />
62
WJEC GCSE Additional Science Teacher’s Notes<br />
Rocket<br />
Launch<br />
mass (kg)<br />
Launch<br />
weight (N)<br />
Launch<br />
thrust (N)<br />
M<strong>in</strong>imum<br />
resultant upwards<br />
force at launch (N)<br />
Falcon 9 340 000 3 400 000 4 500 000 1 100 000<br />
Soyuz-2 310 000 3 100 000 4 000 000 900 000<br />
_Inertia <strong>and</strong> New<strong>to</strong>n’s first law of motion___________<br />
(pages 178–80)<br />
PRACTICAL How well does New<strong>to</strong>n’s first law work on<br />
Earth (page 180)<br />
1. Plot a graph of velocity of <strong>the</strong> glider (y-axis) aga<strong>in</strong>st distance from <strong>the</strong> start of <strong>the</strong> LAT (x-axis).<br />
Graph should be l<strong>in</strong>ear (horizontal) – apart from <strong>the</strong> first portion up <strong>to</strong> <strong>the</strong> first light gate.<br />
2. Draw a best-fit l<strong>in</strong>e through your po<strong>in</strong>ts. If your glider obeys New<strong>to</strong>n’s first law <strong>the</strong>n <strong>the</strong> velocity of<br />
<strong>the</strong> glider will not change as it travels down <strong>the</strong> LAT <strong>and</strong> all <strong>the</strong> velocities will be exactly <strong>the</strong> same.<br />
Graph should be l<strong>in</strong>ear (horizontal) – apart from <strong>the</strong> first portion up <strong>to</strong> <strong>the</strong> first light gate.<br />
3. Does your glider obey New<strong>to</strong>n’s first law<br />
This depends on <strong>the</strong> best-fit l<strong>in</strong>e drawn, but probably yes.<br />
4. Why might <strong>the</strong> velocity of <strong>the</strong> glider change as it moves down <strong>the</strong> track<br />
Air-resistance could slow <strong>the</strong> glider down. The air-track needs <strong>to</strong> be horizontal, o<strong>the</strong>rwise<br />
<strong>the</strong> glider will accelerate/decelerate.<br />
5. Use your data <strong>to</strong> decide how repeatable this experiment is.<br />
Students should plot range-bars on graph <strong>to</strong> judge <strong>the</strong> spread of <strong>the</strong> data.<br />
Fur<strong>the</strong>r experiments:<br />
1. You can <strong>in</strong>troduce more friction <strong>in</strong><strong>to</strong> <strong>the</strong> experiment by turn<strong>in</strong>g down <strong>the</strong> air blower – what happens<br />
<strong>the</strong>n<br />
Introduc<strong>in</strong>g more friction causes <strong>the</strong> glider <strong>to</strong> decelerate <strong>and</strong> slow down.<br />
2. What happens when you <strong>in</strong>crease <strong>the</strong> <strong>in</strong>ertia of <strong>the</strong> glider by stack<strong>in</strong>g masses on it<br />
Velocity is lower (mass is bigger). Eventually, <strong>the</strong> extra weight on <strong>the</strong> glider causes it <strong>to</strong><br />
come <strong>in</strong><strong>to</strong> contact with <strong>the</strong> LAT, caus<strong>in</strong>g friction <strong>and</strong> slow<strong>in</strong>g <strong>the</strong> glider down.<br />
_ Momentum (pages 180–81)_____________________<br />
Questions<br />
3. Calculate <strong>the</strong> momentum of a 5 kg <strong>to</strong>olbag travell<strong>in</strong>g at 7700 m/s.<br />
p = mv = 5 × 7700 = 38 500 kg m/s<br />
4. Calculate <strong>the</strong> momentum of <strong>the</strong> ISS (mass = 400 000 kg), also travell<strong>in</strong>g at 7700 m/s.<br />
63
WJEC GCSE Additional Science Teacher’s Notes<br />
p = mv = 400 000 × 7700 = 3 080 000 000 kg m/s<br />
5. At take-off, <strong>the</strong> Space Shuttle leaves <strong>the</strong> launch <strong>to</strong>wer travell<strong>in</strong>g at 45 m/s. The momentum of <strong>the</strong><br />
Shuttle at this po<strong>in</strong>t is 90 000 000 kg m/s. What is <strong>the</strong> mass of <strong>the</strong> Shuttle at this po<strong>in</strong>t Why isn’t <strong>the</strong><br />
mass of <strong>the</strong> Shuttle constant<br />
p 90 000 000<br />
p = mv m 2 000 000 kg<br />
v 45<br />
As fuel is used up, <strong>the</strong> mass goes down.<br />
6. When <strong>the</strong> solid rocket boosters <strong>and</strong> <strong>the</strong> external fuel tank are jettisoned, <strong>the</strong> Space Shuttle has a<br />
momentum of 140 000 000 kg m/s, <strong>and</strong> a mass of 100 700 kg. What is <strong>the</strong> velocity of <strong>the</strong> Shuttle at this<br />
po<strong>in</strong>t<br />
p = mv <br />
p 140 000 000<br />
v <br />
1390<br />
m/s<br />
m 100 700<br />
7. Use <strong>the</strong> mass <strong>and</strong> momentum <strong>in</strong>formation <strong>in</strong> <strong>the</strong>se <strong>questions</strong> <strong>and</strong> <strong>the</strong> rest of <strong>the</strong> text <strong>to</strong> describe how<br />
<strong>the</strong> mass, velocity <strong>and</strong> momentum of <strong>the</strong> Shuttle change dur<strong>in</strong>g its flight up <strong>to</strong> dock<strong>in</strong>g with <strong>the</strong> ISS.<br />
What is <strong>the</strong> f<strong>in</strong>al momentum of <strong>the</strong> Shuttle just before dock<strong>in</strong>g with <strong>the</strong> ISS<br />
<br />
<br />
<br />
<br />
On launch pad before eng<strong>in</strong>e on: mass constant, velocity zero, momentum zero<br />
At moment of take-off: mass decreas<strong>in</strong>g, velocity <strong>in</strong>creas<strong>in</strong>g, momentum <strong>in</strong>creas<strong>in</strong>g<br />
Up <strong>to</strong> jettison of tanks: mass decreas<strong>in</strong>g, velocity <strong>in</strong>creas<strong>in</strong>g, momentum <strong>in</strong>creas<strong>in</strong>g<br />
Orbit just before dock<strong>in</strong>g (eng<strong>in</strong>es off): mass constant, velocity constant, momentum<br />
constant<br />
_The forces <strong>and</strong> motion at take-off (pages 181–84)____<br />
Discussion po<strong>in</strong>t<br />
A Space Shuttle (mass = 78 000 kg) docks with <strong>the</strong> ISS (mass = 385 471 kg). At <strong>the</strong> moment of dock<strong>in</strong>g <strong>the</strong><br />
ISS is effectively stationary <strong>and</strong> <strong>the</strong> Space Shuttle is mov<strong>in</strong>g at 2 m/s relative <strong>to</strong> <strong>the</strong> ISS. What are <strong>the</strong><br />
relative momentums of <strong>the</strong> Space Shuttle <strong>and</strong> <strong>the</strong> ISS before dock<strong>in</strong>g, <strong>and</strong> what is <strong>the</strong>ir comb<strong>in</strong>ed<br />
momentum after dock<strong>in</strong>g What is <strong>the</strong> effective <strong>in</strong>crease <strong>in</strong> speed of <strong>the</strong> ISS What does this tell you about<br />
momentum <strong>and</strong> collisions<br />
Relative momentum of Space Shuttle = mv = 78 000 × 2 = 156 000 kg m/s<br />
Relative momentum of ISS = 0 kg m/s<br />
Comb<strong>in</strong>ed relative momentum after dock<strong>in</strong>g = 156 000 kg m/s<br />
p 156 000<br />
p = mv v <br />
0.34 m/s<br />
m (78 000 385 471)<br />
Momentum is conserved dur<strong>in</strong>g collisions.<br />
PRACTICAL Investigat<strong>in</strong>g New<strong>to</strong>n’s second law<br />
(pages 182–83)<br />
This experimental demonstration works best us<strong>in</strong>g data-logg<strong>in</strong>g software that calculates<br />
acceleration directly. Remember <strong>to</strong> pre-load <strong>the</strong> glider with weights that can be transferred <strong>to</strong><br />
<strong>the</strong> mass stack so that <strong>the</strong> <strong>to</strong>tal accelerat<strong>in</strong>g mass rema<strong>in</strong>s constant.<br />
1. Calculate values of force/acceleration <strong>in</strong> your table <strong>and</strong> record <strong>the</strong>m.<br />
Calculated values will depend upon data obta<strong>in</strong>ed.<br />
64
WJEC GCSE Additional Science Teacher’s Notes<br />
2. Is <strong>the</strong>re a pattern <strong>in</strong> your results What is <strong>the</strong> average value of force/acceleration How does this<br />
compare <strong>to</strong> <strong>the</strong> mass (<strong>in</strong> kg) of <strong>the</strong> glider plus slotted masses<br />
F/a should be constant with a value (approximately) equal <strong>to</strong> <strong>the</strong> <strong>to</strong>tal accelerat<strong>in</strong>g mass<br />
(glider + mass stack).<br />
3. Plot a graph of resultant force (y-axis) aga<strong>in</strong>st acceleration (x-axis). Confirm that it is a straight l<strong>in</strong>e<br />
<strong>and</strong> draw a best-fit straight l<strong>in</strong>e through your results (start<strong>in</strong>g at <strong>the</strong> orig<strong>in</strong>).<br />
Student graphs.<br />
4. Measure <strong>and</strong> calculate <strong>the</strong> gradient (slope) of <strong>the</strong> graph.<br />
5. Compare your gradient <strong>to</strong> <strong>the</strong> mass (<strong>in</strong> kg) of <strong>the</strong> glider plus <strong>the</strong> slotted masses.<br />
Gradient should (approximately) equal <strong>to</strong>tal accelerat<strong>in</strong>g mass.<br />
Questions<br />
8. A fully laden Soyuz spacecraft (mass = 7150 kg) accelerates away from <strong>the</strong> ISS <strong>to</strong>wards its re-entry<br />
po<strong>in</strong>t with an acceleration of 2 m/s 2 relative <strong>to</strong> <strong>the</strong> ISS. Calculate <strong>the</strong> resultant force on <strong>the</strong> Soyuz<br />
spacecraft.<br />
F = ma = 7150 × 2 = 14 300 N<br />
9. At lift-off, <strong>the</strong> comb<strong>in</strong>ed thrust of <strong>the</strong> SRB <strong>and</strong> ma<strong>in</strong> Shuttle eng<strong>in</strong>es is 30 400 000 N. The <strong>to</strong>tal weight of<br />
<strong>the</strong> Space Shuttle at lift-off is 20 407 000 N, as its mass is 2 040 700 kg.<br />
a Calculate <strong>the</strong> resultant force on <strong>the</strong> Space Shuttle at take-off.<br />
Resultant force = thrust – weight = 30 400 000 – 20 407 000 = 9 993 000 N<br />
b Calculate <strong>the</strong> acceleration of <strong>the</strong> Space Shuttle at take-off.<br />
F = ma <br />
F<br />
a m<br />
<br />
9 993 000<br />
2 040 700<br />
4.9 m/s<br />
2<br />
10. An astronaut is us<strong>in</strong>g <strong>the</strong> manned manoeuvr<strong>in</strong>g unit (MMU) <strong>to</strong> exam<strong>in</strong>e solar panels on <strong>the</strong> ISS. The<br />
MMU generates a small thrust force of 60 N, which accelerates <strong>the</strong> MMU <strong>and</strong> <strong>the</strong> astronaut at 0.25<br />
m/s 2 . Calculate <strong>the</strong> mass of <strong>the</strong> MMU plus <strong>the</strong> astronaut. If <strong>the</strong> astronaut has a mass of 80 kg, what is<br />
<strong>the</strong> mass of <strong>the</strong> MMU<br />
F = ma <br />
F<br />
m a<br />
60 240 kg mass of MMU = 240 – 80 = 160 kg<br />
0.25<br />
_ New<strong>to</strong>n’s second law <strong>and</strong> momentum_____________<br />
(pages 184–87)<br />
Questions<br />
11. Dur<strong>in</strong>g T+200 s <strong>and</strong> T+300 s of a Space Shuttle launch (i.e. between 200 s <strong>and</strong> 300 s after launch), <strong>the</strong><br />
Shuttle (mass = 2 040 700 kg) accelerates from 2600 m/s <strong>to</strong> 4400 m/s.<br />
a Calculate <strong>the</strong> momentum of <strong>the</strong> Shuttle at:<br />
i T+200 s p = mv = 2 040 700 × 2 600 = 5 306 000 000 kg m/s<br />
ii T+300 s p = mv = 2 040 700 × 4 400 = 8 979 000 000 kg m/s<br />
b Calculate <strong>the</strong> change <strong>in</strong> momentum between <strong>the</strong>se times.<br />
65
WJEC GCSE Additional Science Teacher’s Notes<br />
Δp = 8 979 000 000 – 5 306 000 000 = 3 673 000 000 kg m/s<br />
c<br />
Calculate <strong>the</strong> resultant force act<strong>in</strong>g on <strong>the</strong> Shuttle dur<strong>in</strong>g this time.<br />
p<br />
F t<br />
<br />
3 673 000 000<br />
36 731000 N<br />
100<br />
d Dur<strong>in</strong>g this time, <strong>the</strong> Shuttle is both ga<strong>in</strong><strong>in</strong>g altitude <strong>and</strong> los<strong>in</strong>g mass. Expla<strong>in</strong> how both of <strong>the</strong>se will<br />
affect <strong>the</strong> forces act<strong>in</strong>g on <strong>the</strong> Shuttle.<br />
Weight decreases (Shuttle fur<strong>the</strong>r from Earth so g decreases, <strong>and</strong> mass is decreas<strong>in</strong>g). So<br />
resultant force <strong>in</strong>creases (thrust rema<strong>in</strong>s constant until jettison of tanks <strong>and</strong> boosters).<br />
12. In preparation for dock<strong>in</strong>g with <strong>the</strong> ISS, a manned Soyuz spacecraft (mass = 7150 kg) changes velocity<br />
relative <strong>to</strong> <strong>the</strong> ISS from 12.0 m/s <strong>to</strong> 0.5 m/s.<br />
a Calculate <strong>the</strong> change <strong>in</strong> momentum of <strong>the</strong> Soyuz.<br />
Δp = mΔv = 7150 × (12.0 – 0.5) = 82 225 kg m/s<br />
b Calculate <strong>the</strong> resultant decelerat<strong>in</strong>g force act<strong>in</strong>g on <strong>the</strong> Soyuz.<br />
(No time data given) … assum<strong>in</strong>g change of momentum takes 10 s:<br />
p<br />
82 225<br />
F 8222.5 N<br />
t 10<br />
c<br />
The Soyuz has three ‘retro-rockets’ that are used <strong>to</strong> decelerate <strong>the</strong> Soyuz before dock<strong>in</strong>g. Expla<strong>in</strong><br />
how <strong>the</strong>se rockets can decelerate <strong>the</strong> Soyuz.<br />
Retro rockets provide thrust force <strong>in</strong> opposite direction <strong>to</strong> direction of motion of Soyuz –<br />
New<strong>to</strong>n’s Second Law <strong>the</strong>n gives deceleration.<br />
_Touch down! (pages 186–187)___________________<br />
PRACTICAL Mak<strong>in</strong>g a model of a Soyuz descent module<br />
(page 187)<br />
Safety: ensure students are safe <strong>and</strong> stable if <strong>the</strong>y are dropp<strong>in</strong>g objects from a height.<br />
Provide students with a range of different suitable materials <strong>and</strong> resources (glue/scissors/<br />
sellotape/tape measures/s<strong>to</strong>pwatches, etc).<br />
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WJEC GCSE Additional Science Teacher’s Notes<br />
17<br />
The physics of rugby<br />
_ Energy <strong>and</strong> work (pages 189–92)________________<br />
Questions<br />
1. What is meant by ‘work done’<br />
Work is done when energy changes form.<br />
2. What are <strong>the</strong> units of work done<br />
Joules<br />
3. What fac<strong>to</strong>rs dictate <strong>the</strong> amount of work done by a player <strong>in</strong> a l<strong>in</strong>eout lift<strong>in</strong>g a jumper<br />
Number of players lift<strong>in</strong>g <strong>the</strong> jumper, weight of <strong>the</strong> jumper, distance lifted.<br />
4. In a driv<strong>in</strong>g maul, players push<strong>in</strong>g <strong>to</strong> drive <strong>the</strong> maul forward typically push with an average force of<br />
750 N. If <strong>the</strong> driv<strong>in</strong>g maul is pushed 8 m, how much work does a typical player do<br />
work done = force × distance = 750 × 8 = 6000 J<br />
5. Dur<strong>in</strong>g a scrum (Figure 17.3), eight players each push with an average force of 600 N, mov<strong>in</strong>g <strong>the</strong><br />
scrum 2.5 m.<br />
a What is <strong>the</strong> <strong>to</strong>tal force exerted by all eight players<br />
<strong>to</strong>tal force = 8 × 600 = 4800 N<br />
b Calculate <strong>the</strong> <strong>to</strong>tal work done mov<strong>in</strong>g <strong>the</strong> scrum.<br />
work done = force × distance = 4800 × 2.5 = 12 000 J<br />
6. In a head-on driv<strong>in</strong>g tackle, a rugby player does 1650 J of work driv<strong>in</strong>g <strong>the</strong> opponent backwards by 3 m.<br />
Calculate <strong>the</strong> force of <strong>the</strong> tackler.<br />
work done = force × distance<br />
work done 1650<br />
force 550 N<br />
distance 3<br />
7. Calculate <strong>the</strong> distance that a l<strong>in</strong>e-out jumper is lifted if <strong>the</strong> player lift<strong>in</strong>g <strong>the</strong> jumper exerts a force of<br />
950 N <strong>and</strong> does 1520 J of work.<br />
work done = force × distance<br />
work done 1520<br />
distance 1.6 m<br />
force 950<br />
8. What is meant by <strong>the</strong> efficiency of an energy transfer<br />
Efficiency is a measure of how much useful energy comes out from an energy transfer<br />
compared <strong>to</strong> how much <strong>to</strong>tal energy goes <strong>in</strong>.<br />
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WJEC GCSE Additional Science Teacher’s Notes<br />
9. Why is heat normally ‘wasted’ dur<strong>in</strong>g an energy transfer<br />
Dur<strong>in</strong>g energy transfers where heat is produced, <strong>the</strong> heat is normally lost <strong>in</strong><strong>to</strong> <strong>the</strong> surround<strong>in</strong>gs,<br />
<strong>and</strong> cannot be recovered.<br />
10. Why are muscles only 25% efficient<br />
75% of <strong>the</strong> energy produced <strong>in</strong> muscles is wasted as heat as <strong>the</strong> muscles contact <strong>and</strong> relax<br />
11. How do our bodies deal with <strong>the</strong> heat produced by our muscles when we exercise<br />
The excess heat is controlled via homeostasis by sweat<strong>in</strong>g, vasodilation of capillaries near <strong>the</strong><br />
surface of <strong>the</strong> sk<strong>in</strong> <strong>and</strong> <strong>the</strong> flatten<strong>in</strong>g of sk<strong>in</strong> hairs.<br />
PRACTICAL How much work do you do (page 192)<br />
Students need <strong>to</strong> measure <strong>the</strong> distances moved by <strong>the</strong> different weights (vertically) <strong>and</strong> calculate<br />
<strong>the</strong> weights us<strong>in</strong>g weight = mg, or by direct measurement via a new<strong>to</strong>n meter.<br />
Students should take care measur<strong>in</strong>g <strong>the</strong> distances <strong>to</strong> ensure that <strong>the</strong> rulers/tape measure/f<strong>in</strong>gers<br />
do not get caught <strong>in</strong> <strong>the</strong> mach<strong>in</strong>es.<br />
If students are measur<strong>in</strong>g forces directly with a new<strong>to</strong>n meter, loops of str<strong>in</strong>g would be useful <strong>to</strong><br />
put round <strong>the</strong> mach<strong>in</strong>e h<strong>and</strong>les so that <strong>the</strong> new<strong>to</strong>n meters can be attached.<br />
If students calculate <strong>the</strong> efficiency of each mach<strong>in</strong>e, a bar chart would be a suitable way of<br />
illustrat<strong>in</strong>g <strong>the</strong> results.<br />
_ Runn<strong>in</strong>g with a rugby ball – analys<strong>in</strong>g k<strong>in</strong>etic energy<br />
(pages 193–94)<br />
Questions<br />
12. What is meant by k<strong>in</strong>etic energy<br />
The energy possessed by a mov<strong>in</strong>g object.<br />
13. What does <strong>the</strong> k<strong>in</strong>etic energy of a rugby player depend upon<br />
Mass of object <strong>and</strong> velocity of object.<br />
14. If a rugby player jogs at 5 m/s <strong>and</strong> <strong>the</strong>n spr<strong>in</strong>ts at 10 m/s, she doubles her velocity. By what fac<strong>to</strong>r does<br />
her k<strong>in</strong>etic energy <strong>in</strong>crease<br />
KE is proportional <strong>to</strong> v 2 , so if v doubles, KE goes up by a fac<strong>to</strong>r of 2 2 = 4.<br />
15. At a recent Wales squad tra<strong>in</strong><strong>in</strong>g session, <strong>the</strong> spr<strong>in</strong>t<strong>in</strong>g performance of various players was measured<br />
<strong>and</strong> recorded. Table 17.1 summarises <strong>the</strong> f<strong>in</strong>d<strong>in</strong>gs of <strong>the</strong> fitness direc<strong>to</strong>r. Copy <strong>and</strong> complete <strong>the</strong> table<br />
(m<strong>in</strong>us <strong>the</strong> pho<strong>to</strong>s), calculat<strong>in</strong>g <strong>the</strong> maximum k<strong>in</strong>etic energy of each player.<br />
AlunWyn Jones: 4994 J<br />
Shane Williams: 5018 J<br />
Adam Jones: 4588 J<br />
James Hook: 5029 J<br />
16. A st<strong>and</strong>ard (size 5) rugby ball has a mass of 0.44 kg. When kick<strong>in</strong>g from a tee, James Hook can kick<br />
<strong>the</strong> ball with an <strong>in</strong>itial velocity of 24.5 m/s. Calculate <strong>the</strong> <strong>in</strong>itial k<strong>in</strong>etic energy of <strong>the</strong> ball.<br />
68
WJEC GCSE Additional Science Teacher’s Notes<br />
KE = ½ mv 2 = 0.5 × 0.44 × 24.5 2 = 132 J<br />
PRACTICAL Measur<strong>in</strong>g <strong>the</strong> k<strong>in</strong>etic energy of a rugby ball<br />
(page 194)<br />
This is a simple straight-forward task. Students calculate <strong>the</strong> average velocity of <strong>the</strong> ball by<br />
measur<strong>in</strong>g <strong>the</strong> time it takes <strong>to</strong> travel a set distance (this gets more accurate as <strong>the</strong> distance<br />
<strong>in</strong>creases). The ma<strong>in</strong> aim of <strong>the</strong> exercise is <strong>to</strong> get students th<strong>in</strong>k<strong>in</strong>g about a range.<br />
The ma<strong>in</strong> hazard <strong>in</strong> this experiment is be<strong>in</strong>g hit accidentally by a fast-mov<strong>in</strong>g ball – students<br />
can work out suitable control measures <strong>to</strong> m<strong>in</strong>imise harm from this risk.<br />
_ Kick<strong>in</strong>g a ball – an exercise <strong>in</strong> gravitational potential _<br />
energy (pages 194–97)<br />
Questions<br />
17. What is meant by ‘gravitational potential energy’<br />
The energy s<strong>to</strong>red <strong>in</strong> an object due <strong>to</strong> it be<strong>in</strong>g moved through a vertical distance <strong>in</strong> a<br />
gravitational field.<br />
18. Apart from <strong>the</strong> gravitational field strength, what two o<strong>the</strong>r fac<strong>to</strong>rs dictate <strong>the</strong> gravitational potential<br />
energy of a rugby ball<br />
Mass of <strong>the</strong> object <strong>and</strong> vertical distance moved.<br />
19. Rugby balls come <strong>in</strong> three ma<strong>in</strong> sizes: (size 3 (ages 6–9) mass = 0.28 kg, size 4 (ages 10−14) mass =<br />
0.38 kg, size 5 (adult) mass = 0.44 kg). Dur<strong>in</strong>g a media press pho<strong>to</strong>-shoot for a ball sponsor, James<br />
Hook kicks all three balls <strong>to</strong> <strong>the</strong> same height (35 m). If <strong>the</strong> gravitational field strength is 10 N/kg,<br />
calculate <strong>the</strong> gravitational potential energy ga<strong>in</strong>ed by each ball at <strong>the</strong> <strong>to</strong>p of <strong>the</strong> kick.<br />
Size 3: PE = mgh = 0.28 × 10 × 35 = 98 J<br />
Size 4: PE = mgh = 0.38 × 10 × 35 = 133 J<br />
Size 5: PE = mgh = 0.44 × 10 × 35 = 154 J<br />
20. Wales hooker Mat<strong>the</strong>w Rees throws <strong>the</strong> ball <strong>in</strong><strong>to</strong> a l<strong>in</strong>eout from an <strong>in</strong>itial height of 2.0 m. The ball gets<br />
<strong>to</strong> a maximum height of 4.2 m, ga<strong>in</strong><strong>in</strong>g a gravitational potential energy of 9.9 J. If <strong>the</strong> gravitational field<br />
strength is 10 N/kg, calculate <strong>the</strong> mass of <strong>the</strong> ball.<br />
Vertical distance travelled by ball = 4.2 – 2.0 = 2.2 m<br />
PE 9.9<br />
PE mgh m 0.45 kg<br />
gh 10<br />
2.2<br />
PRACTICAL Gravitational potential energy <strong>and</strong> <strong>the</strong> rugby<br />
l<strong>in</strong>eout (page 196–97)<br />
Safety: Ensure that <strong>the</strong> two students lift<strong>in</strong>g <strong>the</strong> third student are capable of lift<strong>in</strong>g <strong>the</strong> jumper,<br />
<strong>and</strong> that <strong>the</strong> jumper is reasonably agile. This activity must be performed on gym or crash mats.<br />
Consult with PE staff before do<strong>in</strong>g this activity. This could be done as a demonstration us<strong>in</strong>g<br />
suitably tra<strong>in</strong>ed students (rugby players). Suitable, non-contact alternatives are suggested us<strong>in</strong>g<br />
different balls.<br />
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WJEC GCSE Additional Science Teacher’s Notes<br />
_ Scrummag<strong>in</strong>g – a case study <strong>in</strong> New<strong>to</strong>n’s third law __<br />
(pages 197–99)<br />
Questions<br />
21. What is New<strong>to</strong>n’s third law<br />
For every action force, <strong>the</strong>re is an equal <strong>and</strong> opposite reaction force.<br />
22. What are <strong>the</strong> names of <strong>the</strong> two forces <strong>in</strong> an <strong>in</strong>teraction pair<br />
Action force <strong>and</strong> reaction force.<br />
23. What are <strong>the</strong> two ma<strong>in</strong> types of force<br />
Contact forces <strong>and</strong> action at a distance forces.<br />
24. Expla<strong>in</strong> why a rugby player <strong>in</strong>volved with push<strong>in</strong>g <strong>in</strong> a maul would only fall on <strong>to</strong> <strong>the</strong> ground if she<br />
slipped or if <strong>the</strong> maul collapsed.<br />
All <strong>the</strong> forces act<strong>in</strong>g on her would be <strong>in</strong> balanced pairs. This means no net resultant force on<br />
her, so she will stay on her feet.<br />
25. Look at <strong>the</strong> follow<strong>in</strong>g diagrams. Sketch each diagram <strong>and</strong> label <strong>the</strong> force <strong>in</strong>teraction pairs <strong>in</strong> each case.<br />
action of spr<strong>in</strong>ter<br />
on block<br />
reaction of block<br />
on spr<strong>in</strong>ter<br />
reaction of<br />
skateboard on<br />
skateboarder<br />
reaction of water<br />
on bottle<br />
action of<br />
skateboarder on<br />
skateboard<br />
action of air<br />
pressure on<br />
water<br />
70
WJEC GCSE Additional Science Teacher’s Notes<br />
18<br />
Cars, <strong>the</strong> Highway Code<br />
<strong>and</strong> collisions<br />
_ Total s<strong>to</strong>pp<strong>in</strong>g distance of a vehicle (pages 200–3)___<br />
Questions<br />
1. For a vehicle, what is <strong>the</strong>:<br />
a th<strong>in</strong>k<strong>in</strong>g distance<br />
The distance that <strong>the</strong> vehicle travels whilst <strong>the</strong> driver sees <strong>the</strong> hazard, th<strong>in</strong>ks about brak<strong>in</strong>g<br />
<strong>and</strong> <strong>the</strong>n actually reacts <strong>to</strong> put <strong>the</strong> brakes on.<br />
b brak<strong>in</strong>g distance<br />
The distance that <strong>the</strong> vehicle moves while <strong>the</strong> brakes are be<strong>in</strong>g applied.<br />
c<br />
<strong>to</strong>tal s<strong>to</strong>pp<strong>in</strong>g distance<br />
<strong>to</strong>tal s<strong>to</strong>pp<strong>in</strong>g distance = th<strong>in</strong>k<strong>in</strong>g distance + brak<strong>in</strong>g distance<br />
2. State <strong>and</strong> expla<strong>in</strong> two fac<strong>to</strong>rs that affect <strong>the</strong> th<strong>in</strong>k<strong>in</strong>g distance of a s<strong>to</strong>pp<strong>in</strong>g car.<br />
Velocity of car, reaction time of <strong>the</strong> driver, driver distractions, use of mobile phone/radio/mp3/<br />
Sat Nav, be<strong>in</strong>g drunk or under <strong>the</strong> <strong>in</strong>fluence of drugs, etc. Each fac<strong>to</strong>r needs a reasonable<br />
explanation.<br />
3. Do you th<strong>in</strong>k that smok<strong>in</strong>g whilst driv<strong>in</strong>g a car affects <strong>the</strong> <strong>to</strong>tal s<strong>to</strong>pp<strong>in</strong>g distance Expla<strong>in</strong> your answer.<br />
Smok<strong>in</strong>g does affect <strong>the</strong> <strong>to</strong>tal s<strong>to</strong>pp<strong>in</strong>g distance because it is a driver distraction, <strong>and</strong> <strong>the</strong> driver<br />
may be hold<strong>in</strong>g <strong>the</strong> cigarette when someth<strong>in</strong>g happens not have that h<strong>and</strong> on <strong>the</strong> wheel.<br />
4. Increased tyre tread greatly reduces <strong>the</strong> brak<strong>in</strong>g distance of a car. Why do you th<strong>in</strong>k that cars are not all<br />
fitted with thick, chunky, off-road tyres with huge treads<br />
Thick, chunky, off-road tyres with huge treads <strong>in</strong>crease <strong>the</strong> friction between <strong>the</strong> tyre <strong>and</strong> <strong>the</strong><br />
road. Increased friction will mean that <strong>the</strong> eng<strong>in</strong>e has <strong>to</strong> do more work, hence fuel consumption<br />
will <strong>in</strong>crease. The ride quality will also be worse as <strong>the</strong> noise will be higher <strong>and</strong> <strong>the</strong> ride will be<br />
more uncomfortable.<br />
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WJEC GCSE Additional Science Teacher’s Notes<br />
19<br />
Us<strong>in</strong>g radioactive decay<br />
_ Radioactive decay (pages 211–213)______________<br />
Questions<br />
1. What are <strong>the</strong> three types of radioactive decay<br />
alpha (α), beta (β) <strong>and</strong> gamma () decay<br />
2. What can ionis<strong>in</strong>g radiation do <strong>to</strong> liv<strong>in</strong>g cells<br />
Damage, mutate or kill cells.<br />
3. What is <strong>the</strong> half-life of a radioactive iso<strong>to</strong>pe<br />
Time taken for half <strong>the</strong> orig<strong>in</strong>al amount of radioactive a<strong>to</strong>ms <strong>to</strong> decay or <strong>the</strong> time taken for <strong>the</strong><br />
activity of a sample <strong>to</strong> halve.<br />
4. After how many half-lives will <strong>the</strong> activity of a radioactive sample be about <strong>the</strong> same as natural<br />
background activity<br />
About 5 half-lives.<br />
5. Why is iridium-192 chosen <strong>to</strong> treat eye sarcoids on horses<br />
Iridium-192 is a beta emitter with a half-life of 74 days – long enough <strong>to</strong> be transferred from<br />
<strong>the</strong> reac<strong>to</strong>r where it is made, but short enough <strong>to</strong> be effectively used for treatment before it is<br />
returned <strong>to</strong> <strong>the</strong> reac<strong>to</strong>r.<br />
6. How long will it take a sample of iridium-192 with an <strong>in</strong>itial activity of 1200 Bq <strong>to</strong> reach an activity of<br />
75 Bq [Remember, <strong>the</strong> half-life of Ir-192 is 74 days.]<br />
After 1 half-life: activity = 1200/2 = 600 Bq<br />
After 2 half-lives: activity = 600/2 = 300 Bq<br />
After 3 half-lives: activity = 300/2 = 150 Bq<br />
After 4 half-lives: activity =150/2 = 75Bq<br />
4 half-lives = 74 × 4 = 296 days<br />
7. A sample of iridium-192 has an activity of 215 Bq, 296 days after it was removed from <strong>the</strong> nuclear<br />
reac<strong>to</strong>r that made it.<br />
a How many half-lives have elapsed <strong>in</strong> 296 days<br />
Number of half-lives = 296/74 = 4<br />
b What was <strong>the</strong> <strong>in</strong>itial activity of <strong>the</strong> sample<br />
Initial activity = ((((215 × 2) × 2) × 2) × 2) = 215 × 2 4 = 3440 Bq<br />
8. Table 19.1 shows <strong>the</strong> radioactive decay of a sample of iod<strong>in</strong>e-131, a radioactive iso<strong>to</strong>pe sometimes<br />
used <strong>to</strong> treat thyroid gl<strong>and</strong> problems.<br />
a Plot a graph of activity (y-axis) aga<strong>in</strong>st time (x-axis).<br />
b Draw a best-fit l<strong>in</strong>e (curve) through your po<strong>in</strong>ts.<br />
72
WJEC GCSE Additional Science Teacher’s Notes<br />
c<br />
Use your graph <strong>to</strong> measure <strong>the</strong> half-life of iod<strong>in</strong>e-131.<br />
PRACTICAL The radioactive decay of protact<strong>in</strong>ium-234<br />
(page 213)<br />
Safety: If you are do<strong>in</strong>g this experiment us<strong>in</strong>g a protact<strong>in</strong>ium genera<strong>to</strong>r, <strong>the</strong>n you must follow<br />
<strong>the</strong> relevant Radioactivity Local Rules for your school <strong>and</strong> <strong>the</strong> relevant CLEAPSS guidance.<br />
A data-logg<strong>in</strong>g GM counter substantially enhances this activity, as <strong>the</strong> activity can be displayed<br />
<strong>in</strong> real-time as a graph.<br />
_ Carbon dat<strong>in</strong>g (page 214)______________________<br />
Questions<br />
9. What is carbon dat<strong>in</strong>g<br />
Carbon dat<strong>in</strong>g is a scientific technique for determ<strong>in</strong><strong>in</strong>g <strong>the</strong> approximate age of an artefact that<br />
conta<strong>in</strong>s once liv<strong>in</strong>g matter us<strong>in</strong>g <strong>the</strong> half-life of <strong>the</strong> naturally occurr<strong>in</strong>g carbon-14 iso<strong>to</strong>pe.<br />
10. Why do you th<strong>in</strong>k that dat<strong>in</strong>g dead organic materials over 60 000 years old is almost impossible us<strong>in</strong>g<br />
carbon dat<strong>in</strong>g<br />
The half-life of carbon-14 is 5730 years – after 5 half-lives (= 28 650 years), <strong>the</strong> percentage of<br />
carbon-14 left <strong>in</strong> <strong>the</strong> sample is very low, after 60 000 years it is so much lower that it cannot be<br />
detected.<br />
11. The Tur<strong>in</strong> Shroud is a holy relic, reputedly <strong>the</strong> shroud used <strong>to</strong> wrap Jesus <strong>in</strong> after his crucifixion. The<br />
shroud appears <strong>to</strong> have <strong>the</strong> image of a man ‘etched’ on one side of <strong>the</strong> cloth. In 1988, three<br />
<strong>in</strong>dependent carbon-dat<strong>in</strong>g labora<strong>to</strong>ries analysed fibres taken from <strong>the</strong> shroud <strong>and</strong> discovered that <strong>the</strong><br />
73
WJEC GCSE Additional Science Teacher’s Notes<br />
samples studied conta<strong>in</strong>ed just over 90% of <strong>the</strong> orig<strong>in</strong>al amount of carbon-14. Use <strong>the</strong> carbon dat<strong>in</strong>g<br />
graph <strong>in</strong> Figure 19.6 <strong>to</strong> estimate <strong>the</strong> age of <strong>the</strong> Tur<strong>in</strong> Shroud.<br />
From <strong>the</strong> graph, approximately 1/6 of a half-life has elapsed, so 5730/6 = 955 years<br />
Sample was produced <strong>in</strong> 1988 – 955 = 1033AD<br />
Discussion po<strong>in</strong>t<br />
There is much debate about <strong>the</strong> au<strong>the</strong>nticity of <strong>the</strong> Tur<strong>in</strong> Shroud. Recent scientific studies have found that<br />
while <strong>the</strong>re is no evidence of any scientific forgery, <strong>and</strong> <strong>the</strong> orig<strong>in</strong> of <strong>the</strong> image on <strong>the</strong> shroud is still<br />
unknown, <strong>the</strong>re is also a suggestion that <strong>the</strong> samples of <strong>the</strong> cloth exam<strong>in</strong>ed <strong>in</strong> 1988 are not representative<br />
of <strong>the</strong> whole shroud. What happens <strong>in</strong> this case The carbon dat<strong>in</strong>g data <strong>in</strong>dicates <strong>the</strong> shroud is a medieval<br />
artefact. Is it possible <strong>to</strong> prove one way or ano<strong>the</strong>r that <strong>the</strong> shroud is real, or a very, very elaborate <strong>and</strong><br />
clever hoax<br />
There are many websites on <strong>the</strong> net that will help <strong>to</strong> <strong>in</strong>itiate debate on this <strong>to</strong>pic. This would make<br />
an excellent homework task: ‘What evidence is <strong>the</strong>re that <strong>the</strong> Tur<strong>in</strong> Shroud is a medieval fake’<br />
TASK Us<strong>in</strong>g radioactive materials (pages 215–19)<br />
1. Which radioactive element from <strong>the</strong> table would you use for an RTG Expla<strong>in</strong> your answer.<br />
Plu<strong>to</strong>nium-238 is normally used for this application, but from <strong>the</strong> list on P215, an alpha<br />
emitter with a half-life of hundreds of years would be suitable – americium-241.<br />
2. Why do you th<strong>in</strong>k that RTGs are only used as <strong>the</strong> power supply on un-manned devices<br />
RTGs are very radioactive <strong>and</strong> produce <strong>to</strong>o much radiation <strong>to</strong> be safe on a manned device.<br />
3. Which radioactive elements would be suitable for use as a radioactive tracer Expla<strong>in</strong> your answer.<br />
The tracer must be a gamma emitter (so that <strong>the</strong> radiation can escape <strong>the</strong> body) with a short<br />
half-life (so that <strong>the</strong> radiation dose received by <strong>the</strong> patient is m<strong>in</strong>imised) – technicium-99.<br />
4. Why is it important that <strong>the</strong> radioactive tracer that is used has a very short half-life<br />
The tracer must have a short half-life so that <strong>the</strong> radiation dose received by <strong>the</strong> patient is<br />
m<strong>in</strong>imised.<br />
5. For each of <strong>the</strong> follow<strong>in</strong>g forms of radio<strong>the</strong>rapy suggest <strong>and</strong> expla<strong>in</strong> which radioiso<strong>to</strong>pe(s) you would<br />
choose:<br />
a external beam radio<strong>the</strong>rapy<br />
A gamma emitter with a half-life measured <strong>in</strong> hundreds of years would be needed so<br />
that <strong>the</strong> beam of gamma rays rema<strong>in</strong>ed as constant as possible – Europium-152 or<br />
Barium-133.<br />
b brachy<strong>the</strong>rapy<br />
A beta emitter with a half-life of tens of days would be suitable – iridium-192.<br />
c<br />
unsealed source radio<strong>the</strong>rapy<br />
A beta emitter with a short half-life – iod<strong>in</strong>e-131.<br />
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WJEC GCSE Additional Science Teacher’s Notes<br />
6. Expla<strong>in</strong> what safety precautions a specialist radio<strong>the</strong>rapy nurse would have <strong>to</strong> take if treat<strong>in</strong>g a<br />
patient us<strong>in</strong>g external beam radio<strong>the</strong>rapy.<br />
The safety precautions are:<br />
leave <strong>the</strong> room when <strong>the</strong> gamma beam is on<br />
observe patient through lead glass screen<br />
focus <strong>the</strong> beam carefully<br />
control beam exposure so dose is effective but m<strong>in</strong>imised.<br />
7. Which radioiso<strong>to</strong>pes would you use for leak detection<br />
Gamma emitter with a short half-life is needed – technicium-99.<br />
8. Why is it important that radioso<strong>to</strong>pes used <strong>in</strong> leak detection have short half-lives<br />
Half-life must be short <strong>to</strong> ensure that <strong>the</strong> dose received by <strong>the</strong> general public <strong>and</strong> <strong>the</strong><br />
opera<strong>to</strong>rs is very small.<br />
9. Why are beta sources used for thickness control applications<br />
The <strong>in</strong>tensity of beta particles pass<strong>in</strong>g through <strong>the</strong> paper will be affected by <strong>the</strong> thickness of<br />
<strong>the</strong> paper. No alpha particles would get through even <strong>the</strong> th<strong>in</strong>nest paper, <strong>and</strong> gamma rays<br />
would be unaffected by <strong>the</strong> paper.<br />
10. State with a reason which radioiso<strong>to</strong>pe you would choose for use <strong>in</strong> a thickness control mach<strong>in</strong>e.<br />
How would you arrange this source under <strong>the</strong> sheet<br />
Strontium-90 would be a good source for a thickness detec<strong>to</strong>r as it is a beta emitter with a<br />
suitable half-life where <strong>the</strong> <strong>in</strong>tensity of <strong>the</strong> beta particle beam would not change<br />
significantly from day <strong>to</strong> day. The source would be extended underneath <strong>and</strong> across <strong>the</strong> full<br />
width of <strong>the</strong> paper so that <strong>the</strong> detec<strong>to</strong>r sampled <strong>the</strong> full width.<br />
11. Why is it important that <strong>the</strong> Geiger counter is long enough <strong>to</strong> stretch across <strong>the</strong> whole sheet<br />
The Geiger counter needs <strong>to</strong> sample across <strong>the</strong> whole of <strong>the</strong> width of <strong>the</strong> sheet <strong>to</strong> ensure it is<br />
an even thickness.<br />
12. Which radioiso<strong>to</strong>pes would you use for metal weld detection Expla<strong>in</strong> your answer.<br />
A gamma emitter with a long half-life so that <strong>the</strong> gamma beam <strong>in</strong>tensity did not change<br />
significantly from day-<strong>to</strong>-day – Europium-152 or Barium-133.<br />
13. What precautions would <strong>the</strong> opera<strong>to</strong>r need <strong>to</strong> take when analys<strong>in</strong>g a metal weld<br />
<br />
<br />
<br />
<br />
<br />
<br />
Keep (very small) source <strong>in</strong> sealed lead conta<strong>in</strong>er when not <strong>in</strong> use<br />
M<strong>in</strong>imise time <strong>in</strong> use<br />
Collimate beam (so it only goes <strong>in</strong> one direction)<br />
St<strong>and</strong> away from <strong>the</strong> beam when <strong>in</strong> use<br />
Ensure no o<strong>the</strong>r people are <strong>in</strong> <strong>the</strong> way of <strong>the</strong> beam<br />
Wear lead apron/tabard<br />
14. Why would α <strong>and</strong> β radioiso<strong>to</strong>pes be unsuitable for this application<br />
Alpha <strong>and</strong> beta radiation would not penetrate through <strong>the</strong> weld.<br />
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WJEC GCSE Additional Science Teacher’s Notes<br />
15. Expla<strong>in</strong> which radioiso<strong>to</strong>pes you could use for a mach<strong>in</strong>e that sterilises medical <strong>in</strong>struments.<br />
A gamma emitter with a long half-life so that <strong>the</strong> gamma beam <strong>in</strong>tensity did not change<br />
significantly from day-<strong>to</strong>-day – Europium-152 or Barium-133.<br />
16. Why is it important that <strong>the</strong> sterilis<strong>in</strong>g mach<strong>in</strong>e is surrounded by a thick lead shield<br />
To m<strong>in</strong>imise dose/exposure <strong>to</strong> <strong>the</strong> opera<strong>to</strong>rs.<br />
17. Expla<strong>in</strong> why americium-241 would be a good choice for <strong>the</strong> radioiso<strong>to</strong>pe <strong>in</strong> a smoke detec<strong>to</strong>r.<br />
It is an alpha emitter with a long half-life so that <strong>the</strong> beam <strong>in</strong>tensity does not drop<br />
significantly from day-<strong>to</strong>-day.<br />
18. Why doesn’t a smoke alarm need a lead shield around it<br />
It is an alpha emitter <strong>and</strong> so <strong>the</strong> alpha particles are absorbed <strong>in</strong>side <strong>the</strong> detec<strong>to</strong>r by <strong>the</strong> walls<br />
of <strong>the</strong> radioactive source holder <strong>and</strong> <strong>the</strong> plastic cover.<br />
Discussion po<strong>in</strong>t<br />
Some types of food are treated <strong>in</strong> <strong>the</strong> same way. Strawberries, onions, pota<strong>to</strong>es <strong>and</strong> spices can all be<br />
sterilised <strong>in</strong> this way. By kill<strong>in</strong>g <strong>the</strong> bacteria on <strong>the</strong> food products <strong>the</strong>y can have a substantially longer<br />
shelf-life. Would you like <strong>to</strong> eat irradiated strawberries<br />
An <strong>in</strong>terest<strong>in</strong>g discussion pitt<strong>in</strong>g scientific underst<strong>and</strong><strong>in</strong>g aga<strong>in</strong>st irrational fear!<br />
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WJEC GCSE Additional Science Teacher’s Notes<br />
20<br />
Nuclear power<br />
Discussion po<strong>in</strong>t<br />
There are lots of resources onl<strong>in</strong>e that show <strong>the</strong> possible effects of <strong>the</strong> La Palma mega-tsunami. You might<br />
like <strong>to</strong> try: www.guardian.co.uk/flash/cumbre_vieja_tsunami.swf<br />
Both of <strong>the</strong>se discussion po<strong>in</strong>ts are based on student op<strong>in</strong>ion.<br />
1. Do you th<strong>in</strong>k that <strong>the</strong> potential for natural disaster outweighs <strong>the</strong> need for secure, large-scale, carbonneutral<br />
electricity<br />
You may like <strong>to</strong> po<strong>in</strong>t out that secure, large-scale, carbon neutral electricity need not<br />
exclusively come from nuclear power.<br />
2. Global warm<strong>in</strong>g or nuclear disaster – which is worse <strong>in</strong> your view<br />
Is it a choice between one or <strong>the</strong> o<strong>the</strong>r<br />
_Where does nuclear power come from ____________<br />
(pages 222–23)<br />
Questions<br />
1. Write nuclear equations for <strong>the</strong> follow<strong>in</strong>g decays:<br />
a uranium-235,<br />
235<br />
231<br />
92 U , also an alpha particle emitter, decay<strong>in</strong>g <strong>in</strong><strong>to</strong> thorium-231, 90 Th .<br />
235<br />
231<br />
92 U 90 Th <br />
4<br />
2<br />
He<br />
b carbon-14,<br />
14<br />
6<br />
C <br />
14<br />
7<br />
14 14<br />
6 C , is a beta emitter, decay<strong>in</strong>g <strong>in</strong><strong>to</strong> nitrogen-14, 7 N .<br />
N <br />
0<br />
-1e<br />
2. Use a Periodic Table or a Table of Nuclides (try:<br />
http://en.wikipedia.org/wiki/Table_of_nuclides_(complete)) <strong>to</strong> write nuclear equations <strong>to</strong> determ<strong>in</strong>e <strong>the</strong><br />
decay product of <strong>the</strong> follow<strong>in</strong>g iso<strong>to</strong>pes:<br />
a alpha emitters:<br />
241 237 4<br />
i americium-241 95 Am 93 Np 2He<br />
ii polonium-210<br />
iii radon-222<br />
iv radium-226<br />
210<br />
206<br />
84 Po 82Pb<br />
<br />
222<br />
218<br />
86 Rn 84Po<br />
<br />
226<br />
222<br />
88 Ra 86Rn<br />
<br />
4<br />
2<br />
4<br />
2<br />
4<br />
2<br />
He<br />
He<br />
He<br />
236 232 4<br />
v plu<strong>to</strong>nium-236 94 Pu 92U<br />
2He<br />
b beta emitters:<br />
3 3<br />
i hydrogen-3 (tritium) - 0 1 H 2He<br />
1e<br />
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WJEC GCSE Additional Science Teacher’s Notes<br />
ii phosphorus-32<br />
32<br />
15<br />
P <br />
32<br />
16<br />
S <br />
e - 0 1<br />
iii nickel-63<br />
iv strontium-90<br />
63<br />
28<br />
90<br />
38<br />
Ni <br />
Sr <br />
63<br />
29<br />
90<br />
39<br />
Cu <br />
Y <br />
e - 0 1<br />
e - 0 1<br />
24 24<br />
v sodium-24 - 0 11 Na 12Mg<br />
1e<br />
_ Nuclear fission (pages 224–27)__________________<br />
Discussion po<strong>in</strong>ts<br />
1. You do <strong>the</strong> maths: 1 a<strong>to</strong>m of U-235 has a mass of 3.9 × 10 –25 kg. How many a<strong>to</strong>ms of U-235 are <strong>the</strong>re<br />
<strong>in</strong> 1 kg If each a<strong>to</strong>m’s nucleus can emit 3.2 × 10 –11 J of heat energy, how much heat energy could 1 kg<br />
of U-235 produce<br />
1<br />
number of a<strong>to</strong>ms 2.6 10<br />
-25<br />
3.9 10<br />
heat energy = 2.6 × 10 24 × 3.2 × 10 –11<br />
E = 8.3 × 10 13 J<br />
24<br />
2. Is nuclear power from fission worth it <strong>in</strong> terms of energy 1 kg of U-235 could produce about 83 TJ<br />
(83 × 10 12 J) of energy. By comparison, 1 kg of best coal could produce 35 MJ (35 × 10 6 J). How much<br />
coal would you have <strong>to</strong> burn <strong>to</strong> get <strong>the</strong> same amount of energy as 1 kg of uranium-235<br />
energy produced by 1kg of uranium<br />
amount of coal needed <br />
energy produced by 1kg of coal<br />
= 2.4 × 10 6 kg (i.e. 2.4 million kg)<br />
3. Are <strong>the</strong>re any o<strong>the</strong>r considerations when compar<strong>in</strong>g coal <strong>and</strong> uranium<br />
For coal it is <strong>the</strong> environmental impacts of extraction <strong>and</strong> CO 2 output.<br />
For nuclear it is <strong>the</strong> environmental impact of radioactive waste (highly radioactive for hundreds<br />
of millions of years).<br />
Questions<br />
3. Use a Periodic Table or a Table of Nuclides <strong>to</strong> write nuclear equations <strong>to</strong> summarise <strong>the</strong> follow<strong>in</strong>g<br />
fission reactions <strong>in</strong>side a nuclear fuel rod, occurr<strong>in</strong>g from <strong>the</strong> fission of uranium-235 from one neutron.<br />
The fission products are:<br />
a xenon-140, strontium-94 <strong>and</strong> two neutrons<br />
235 140 94 1<br />
92 U 54Xe<br />
38 Sr 20<br />
b rubidium-90, caesium-144 <strong>and</strong> two neutrons<br />
235 90 144 1<br />
92 U 37Rb<br />
55 Cs 20<br />
n<br />
n<br />
c<br />
lanthanum-146, brom<strong>in</strong>e-87 <strong>and</strong> three neutrons.<br />
235 146 87 1<br />
92 U 57La<br />
35 Br 30<br />
n<br />
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WJEC GCSE Additional Science Teacher’s Notes<br />
Discussion po<strong>in</strong>t<br />
You can f<strong>in</strong>d out about how nuclear reac<strong>to</strong>rs work by search<strong>in</strong>g onl<strong>in</strong>e us<strong>in</strong>g key-words such as ‘nuclear<br />
power plant’, ‘animation’ <strong>and</strong> ‘applet’. Your teacher may show you one of <strong>the</strong>se. How is <strong>the</strong> heat energy<br />
generated by <strong>the</strong> reac<strong>to</strong>r transformed <strong>in</strong><strong>to</strong> electricity<br />
The heat from <strong>the</strong> reac<strong>to</strong>r is used <strong>to</strong> heat water <strong>to</strong> make steam, which turns a turb<strong>in</strong>e-genera<strong>to</strong>r –<br />
<strong>the</strong> same as <strong>in</strong> a conventional power station.<br />
Questions<br />
4. What is <strong>the</strong> ma<strong>in</strong> fuel used <strong>in</strong> a nuclear reac<strong>to</strong>r<br />
Uranium-235<br />
5. What is a ‘cha<strong>in</strong> reaction’<br />
The neutrons released from <strong>the</strong> fission of one U-235 a<strong>to</strong>m can <strong>in</strong>itiate <strong>the</strong> fission of o<strong>the</strong>r<br />
U-235 a<strong>to</strong>ms, <strong>and</strong> so on.<br />
6. Why does a nuclear reac<strong>to</strong>r need a modera<strong>to</strong>r<br />
The fission of U-235 by neutrons requires <strong>the</strong> neutrons <strong>to</strong> be slow-mov<strong>in</strong>g – <strong>the</strong> modera<strong>to</strong>r,<br />
usually water, is used <strong>to</strong> slow <strong>the</strong> neutrons down <strong>in</strong>creas<strong>in</strong>g <strong>the</strong> likelihood of fission events.<br />
7. How can a nuclear power station reac<strong>to</strong>r be controlled<br />
Control rods, usually made of graphite or boron, absorb neutrons. Rais<strong>in</strong>g or lower<strong>in</strong>g <strong>the</strong><br />
control rods controls <strong>the</strong> rate of fission <strong>and</strong> hence <strong>the</strong> power output of <strong>the</strong> reac<strong>to</strong>r.<br />
8. Why is <strong>the</strong> reac<strong>to</strong>r encased <strong>in</strong>side a steel vessel surrounded by a thick concrete conta<strong>in</strong>ment structure<br />
To m<strong>in</strong>imise <strong>the</strong> escape of highly energetic <strong>and</strong> penetrat<strong>in</strong>g gamma rays (produced <strong>in</strong>side <strong>the</strong><br />
reac<strong>to</strong>r) escap<strong>in</strong>g <strong>in</strong><strong>to</strong> <strong>the</strong> local environment.<br />
9. Why do spent fuel rods need <strong>to</strong> be s<strong>to</strong>red under water <strong>in</strong> ponds with<strong>in</strong> <strong>the</strong> conta<strong>in</strong>ment structure<br />
The spent fuel rods are still highly radioactive <strong>and</strong> produce large amounts of heat. The water <strong>in</strong><br />
<strong>the</strong> ponds is used <strong>to</strong> cool <strong>the</strong> fuel rods.<br />
10. Draw a flow chart show<strong>in</strong>g how electricity is generated by nuclear fission <strong>in</strong> a nuclear power station.<br />
Fission of<br />
U-235<br />
Heats water<br />
produc<strong>in</strong>g steam<br />
Steam turns turb<strong>in</strong>e<br />
which turns genera<strong>to</strong>r<br />
Electricity produced <strong>and</strong><br />
delivered <strong>to</strong> <strong>the</strong> National<br />
Grid<br />
_ Is <strong>the</strong>re ano<strong>the</strong>r way (pages 227–30)____________<br />
Questions<br />
11. What is nuclear fusion<br />
Nuclear fusion is <strong>the</strong> jo<strong>in</strong><strong>in</strong>g <strong>to</strong>ge<strong>the</strong>r of lighter nuclei <strong>to</strong> make heavier ones <strong>and</strong> dur<strong>in</strong>g <strong>the</strong><br />
process emitt<strong>in</strong>g large amounts of energy.<br />
12. Inside <strong>the</strong> core of <strong>the</strong> Sun, what are <strong>the</strong> particles <strong>in</strong>volved with nuclear fusion<br />
Inside <strong>the</strong> Sun, hydrogen nuclei (pro<strong>to</strong>ns) fuse <strong>to</strong>ge<strong>the</strong>r dur<strong>in</strong>g <strong>the</strong> process of nuclear fusion.<br />
49
WJEC GCSE Additional Science Teacher’s Notes<br />
13. Why are high temperatures <strong>and</strong> pressures needed for nuclear fusion<br />
High temperatures <strong>and</strong> pressures are needed <strong>to</strong> ensure that enough pro<strong>to</strong>ns get close enough for<br />
<strong>the</strong> process of nuclear fusion <strong>to</strong> occur.<br />
14. What are deuterium <strong>and</strong> tritium How are <strong>the</strong>y different <strong>to</strong> ‘normal’ hydrogen<br />
Deuterium <strong>and</strong> tritium are iso<strong>to</strong>pes of hydrogen. They both conta<strong>in</strong> a s<strong>in</strong>gle pro<strong>to</strong>n (like normal<br />
hydrogen) but a deuterium nucleus has an extra neutron, <strong>and</strong> tritium has two extra neutrons.<br />
15. What is a plasma<br />
A plasma is an ionised gas.<br />
16. How is <strong>the</strong> plasma of deuterium <strong>and</strong> tritium conf<strong>in</strong>ed <strong>in</strong>side a <strong>to</strong>kamak reac<strong>to</strong>r<br />
A <strong>to</strong>roidal (r<strong>in</strong>g doughnut) shaped magnetic field conf<strong>in</strong>es <strong>the</strong> plasma <strong>in</strong>side <strong>the</strong> <strong>to</strong>kamak<br />
reac<strong>to</strong>r.<br />
17. How are <strong>the</strong> high temperatures generated with<strong>in</strong> a <strong>to</strong>kamak reac<strong>to</strong>r<br />
The high temperatures are generated by pass<strong>in</strong>g huge electric currents through <strong>the</strong> plasma.<br />
18. How could <strong>the</strong> energy of a nuclear fusion reac<strong>to</strong>r be used <strong>to</strong> produce electricity<br />
The high k<strong>in</strong>etic energy of <strong>the</strong> neutrons emitted dur<strong>in</strong>g <strong>the</strong> fusion process could be used <strong>to</strong> heat<br />
water as <strong>the</strong> basis of electricity generation.<br />
19. Why do nuclear fusion reac<strong>to</strong>rs need a lot of shield<strong>in</strong>g<br />
Nuclear fusion reac<strong>to</strong>rs produce huge numbers of high energy neutrons which need <strong>to</strong> be<br />
conta<strong>in</strong>ed <strong>to</strong> prevent damage <strong>to</strong> <strong>the</strong> human opera<strong>to</strong>rs.<br />
Discussion po<strong>in</strong>t<br />
O<strong>the</strong>r rival nuclear fusion reac<strong>to</strong>r designs (such as HiPER – <strong>the</strong> European High Power laser Energy<br />
Research facility) would use high powered lasers <strong>to</strong> heat a small quantity of deuterium <strong>and</strong> tritium <strong>in</strong>side a<br />
small spherical pellet. Such designs have been shown <strong>to</strong> work, produc<strong>in</strong>g small quantities of nuclear fusion.<br />
The trick is <strong>to</strong> get a cont<strong>in</strong>uous feed of fusion fuel <strong>in</strong><strong>to</strong> <strong>the</strong> laser beams <strong>in</strong> a short enough time <strong>to</strong> susta<strong>in</strong> <strong>the</strong><br />
reaction. Use <strong>the</strong> <strong>in</strong>ternet <strong>to</strong> f<strong>in</strong>d out about nuclear fusion reac<strong>to</strong>rs that use lasers (<strong>the</strong> process is called<br />
Inertial Conf<strong>in</strong>ement Fusion or ICF). How might it compare <strong>to</strong> <strong>to</strong>kamak based reac<strong>to</strong>rs<br />
Us<strong>in</strong>g a search eng<strong>in</strong>e with <strong>the</strong> key words ‘<strong>in</strong>ertial conf<strong>in</strong>ement fusion’ will f<strong>in</strong>d many different<br />
websites devoted <strong>to</strong> Laser ICF. Tokamak reac<strong>to</strong>rs currently represent <strong>the</strong> best ‘chance’ of<br />
produc<strong>in</strong>g a commercially viable nuclear fusion reac<strong>to</strong>r.<br />
50