Teachers Guide Scientriffic 81 - CSIRO

Blooming bicarbonate
CurriCulum links
Science understanding: Year 4 Earth and space sciences, Year
4 chemical sciences
Science inquiry skills: Foundation – Year 4 Questioning and
predicting, planning and conducting
Aim
To demonstrate stalactite growth using sodium bicarbonate
and water.
BACkground
Read the article ‘Underground wonderland’ on pages
18–19 of Scientriffic.
You will need
• Hot water (from a tap)
• 2 glass jars
• 2 metres of white cotton thread
• 2 paper clips
• Bicarb soda (sodium bicarbonate)
• Teaspoon
• Food colouring – two different colours
• A jar lid
NAME ______________________________________________
whAt to do
1. Carefully pour some hot tap water into the two jars
until they are about one-third full.
2. Add three heaped teaspoons of bicarb soda to one of
the jars. Stir the powder until it has dissolved.
3. Continue adding and stirring bicarb soda into the jar,
one teaspoon at a time, until no more will dissolve.
This is called a saturated solution.
4. Repeat steps 2 and 3 with the second jar of water.
5. Put the jars on a flat surface, such as a table or a
window, where they can be left to sit undisturbed for a
few days.
6. Take the piece of cotton thread and fold it in half two
or three times, until you have a piece that is about 30
centimetres long.
7. Put the entire thread into one of the jars and soak it in
the solution.
8. Take out the thread and place one end into one of the
jars so it is submerged in the solution. Use a paper clip
to secure it to the side of the jar. The thread shouldn’t
touch the bottom the jar.
2 St | www.csiro.au/scientriffic | Scientriffic Teacher’s Guide | September 2012
9. Place the other end of the thread into the solution
in the second jar, holding it in place with another
paperclip. Let the thread droop a little in between the
jars – don’t pull it tight.
10. Put a jar lid between the two jars to catch any liquid
that drips off the thread.
11. Add two drops of food colouring to one of the jars.
12. Add two drops of another colour of food colouring to
the other jar.
13. Draw a picture of the jars and thread in the space
below, describing what you think it will look like in
two days.
14. Leave the jars for at least two days and observe what
happens. Draw a picture of your results in the table.
15. When you have finished the experiment, answer
the questions at the bottom of the page in your
workbook.
PrediCtion
results
PHoToCoPYING PERMITTED FoR PERSoNAL, HoME AND CLASSRooM USE. CoPYRIGHT © CSIRo 2012
Draw a picture of what you think will happen to the
solution inside the jars:
Draw a picture of the jars and the string after two days:
Questions
• What happened to the solution inside the jar?
• How did the food colouring affect the thread and the
crystals?
• How do you think this experiment can be linked to
cave formations such as stalactites and stalagmites?