The Electrical experimenter

850 ELECTRICAL EXPERIMENTER April. 1918
Experiment No. 113.
Silver and Copper With Nitric Acid.
PUT
into an evaporating dish a piece
of silver and pour over it 2 cc.
(measured) of nitric acid. Place the
dish on a ring stand over asbestos
or iron gauze and apply heat until
strong fumes begin to appear ; then remove
the lamp from beneath the dish and permit
the action to continue as long as it will.
Mr. D. J. Thomson in the February issue
Iroporottng dish
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Experimental Chemistry
By ALBERT W. WILSDON
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How Apparatus Is Arranged for the Preparation
of Silver Nitrate.
of the Electrical Experimenter, page 699.
described a method of preparing pure silver
from a silver coin. The editorial note appended
thereto should be read carefully.
For the purpose of illustrating the action
which takes place upon the decomposition
of a silver coin as described in the article
above mentioned, let us mix 90 per cent of
silver and 10 per cent of copper (which is
approximately the composition of a 10-cent
piece). Place these in an evaporating dish
and add 2 cc (measured) of nitric acid.
What action do you notice first? What
color has the liquid? Examine some silver
nitrat and copper nitrat in solid form and
in solution, and see if you can explain the
color you
due to the
obtained.
copper or
Is
the
the discoloration
silver? Are any
crystals formed in your solution? If so,
describe
try and
them as
identify
to shape, color, etc., and
them. What does your
solution apparently contain?
When the action wholly stops, remove
any solid particles and add 10 or 15 cc. of
water, stir it till any crystals dissolve; if
the solution is not clear, filter it; pour it
into a clean tube (saving a little in another
tube for comparison), and suspend in the
solution a copper wire (No. 9 or 10 B. & S.)
made bright by running a piece of emery
paper over it, or in place of the wire use
a strip of copper. See Figs. 110 and 111
Note any immediate action ; then allow the
solution to stand, proceeding with other
experiments.
Strip of. Cu in
AyMo, "
Fig III ©
Arrangement of Test Tubes for Making Observations
of Actions of Different Metals on
Various Solutions
At the end of half an hour or so examine
the contents of the tube with care, noting
Twenty-Third Lesson
the color, luster and shape of the deposit.
To ascertain wr hether it is amorphous or
crystallin, examine some of it under a
microscope. Has the solution changed
color? Compare with the previous solution.
If so, state how, and account for it.
Notice whether that part of the copper wire
in the liquid has been reduced in size. Try
and account for any change in the size of
the wire.
Wash the deposit from the wire into a
dish, return the wire, and wash the deposit
several times by decantation, with stirring,
and when every trace of copper nitrat solution
is washed out, put away the silver in
a vial and label it for future use, reserving
a very little to dissolve in a few drops of
nitric acid. The ionic equation for the
action of nitric acid on silver is
+ _ + _
3 Ag + 4H + 4NOs = 3 Ag+3NO„ + 2H 2 + NO
In the above, 3 atoms of silver replace
3 hydrogen ions and become 3 silver ions
4 hydrogen ions unite with 2 oxygen ions
(thus breaking up one NOa ion), seizing
upon enough oxygen to combine with it,
forming two molecules of water and leaving
a molecule of the gas-NO.
The ionic equation for copper acting on
the solution of silver nitrat is:
+ — ++ —
Cu + 2Ag + 2NO, - Cu + 2N0 3 + 2Ag
The common parts, 2N0 3 , may be cancelled.
One copper atom forms a copper
ion and deposits two atoms of silver. Atoms
and ions thus change places.
Experiment No. 114.
Copper and Lead With Nitric Acid.
Place 2 grams of copper scraps in a dish
and pour over them 2 cc. of nitric acid. If
the acid is concentrated, no heat need be
applied.
As in the previous experiment notice all
the phenomena of the gaseous, liquid and
solid products.
When chemical action has stopt, add 10
or IS cc. of water and stir the mixture
then filter it (unless it is perfectly clear) ;
save 2 or 3 cc. of it to compare as to color
with that obtained by the next process. The
remainder is to be poured into a narrow
tube and a strip of sheet lead or a piece of
lead wire (No. 9 or 10 B. & S.), made
bright by tiling or by sand-papering, hung
in the liquid and extended to the bottom.
If after a few minutes no deposit is noted,
warm the tube and let it stand for half an
hour, noting occasionally whether anything
is depositing on the wire or at the bottom.
If much free acid, due to adding an excess
of nitric acid, is present, considerable effervescence
will ensue. This is to be avoided
by measuring the acid at the beginning of
the experiment and making sure that all
has reacted with the copper. If the deposit
on the wire is small, it may be left for
twenty-four hours.
Finally take out the wire, scrape off the
deposit in a dish, and return the wire after
noting the relative sizes now and at the
beginning. Filter the liquid and compare
its color with the sample taken earlier in
the experiment. Try and account for any
difference. Any deposit at the bottom of
the tube should be put with that taken
from the wire and washed several times by
decantation, with stirring; then put it into
a vial or tube and label it. except a little
; ;
that should be placed in a dish and tested
with a few drops of nitric acid. Think out
carefully all the results obtained and make
full notes, with an explanation of all phenomena
and reactions ; also try and reason
out the two ionic equations.
Experiment No. 115.
Lead and Zinc With Nitric Acid.
Into a porcelain dish put about 2 grams
of lead fiber or a piece of sheet lead, about
a quarter of an inch square, and pour over
P/cftfwm \
anode X
Fig. 1/2
P/otinum
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In electrolytic Woi K, tlectrodes or Platinum
Should Be Employed Similar to the Ones
Here Illustrated.
it 5 or 10 cc of nitric acid which has been
diluted with an equal volume of water.
Heat the dish for five minutes ; then as
soon as the action stops add 10 cc. water,
stir it, take out any excess of metal, and
filter the solution unless it is clear. Hang
in the narrow tube containing the nitrat
a piece of zinc wire (No. 9 or 10 B. & S.)
or a strip of zinc, leaving it for at least
half an hour (or, better, for twenty-four
hours). Then take out the wire, remove
the residue to a dish, wash it by decantation
several times, and put it into a vial
and label it.
Make as close observations and take as
full notes on all parts of this experiment
as you did in the two previous ones. Examine
specimens of lead nitrat and zinc
nitrat both in solution and in the solid
state. Of two elements, the one that drives
the other out of solution is said to be
electropositive to the one deposited or
driven out. Of the nitrates in the last
three experiments, namely, lead, silver and
zinc, and hydrogen (nitric acid), arrange
the elements according to their electrochemical
affinities, placing the symbol of
the most positive or the (•Ins first, then in
regular order to the most negative or
minus. A negative ion is driven out of
solution by a more positive ion, each ion
replacing other ions according to its
(Continued on page 861)
•' ~;se
fig //J
To source of
current
A Simple, Yet Rugged, Electrolytic Apparatus
Which the Amateur Electro-Chemist Can
Construct in a Few Minutes' Time and Which
Is Adjustable for Different Size Bearers.