288 DIY Science: Illustrated Guide to Home Chemistry Experiments
POCEDURER
1.f you have not already done so, put on your splash I
goggles, gloves, and protective clothing.
- Weigh about 15 g of magnesium sulfate heptahydrate
and transfer it to the beaker. - Fill the beaker nearly full with distilled water and stir
until the magnesium sulfate dissolves completely.
wHAGNESIU ym m SULfATE?
Pure water does not conduct electricity. Dissolving
magnesium sulfate—which is cheap, readily available,
and electrochemically inert—produces a solution of
charged magnesium ions and sulfate ions that allows the
solution to conduct electricity. Some other ionic salts,
such as sodium bicarbonate, can be substituted for the
magnesium sulfate, but not all ionic salts can be used. For
example, if you use sodium chloride (common table salt),
chlorine gas is produced at one electrode and sodium
hydroxide (lye) at the other electrode. The electrochemical
potentials of the magnesium and sulfate ions are such that
they act only to increase the conductivity of the solution,
and otherwise remain unaffected by the electrolysis.11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
CUTIOA nS
Although the quantities produced are very small, this
experiment produces hydrogen gas, which is very
flammable, and oxygen gas, which causes vigorous
combustion of any burning substance. Wear splash
goggles, heavy-duty gloves, and protective clothing.z
4.ill one of the test tubes completely with the magnesium F
sulfate solution, place your finger or thumb over the
tube, invert it, and immerse it in the beaker. Make
sure the tube is completely filled with the solution and
contains no air bubble. Repeat this procedure for the
second test tube, and then use the rubber band to
secure the two tubes together. Make sure the mouths of
the test tubes are at least several centimeters below the
surface of the solution.- Repeat step 4 with the second pair of test tubes.
- Place the beaker on the base of the ring stand, with its
center under the clamp. - Gently lower the 9V transistor battery into the beaker,
with its electrodes up. You’ll see a trail of bubbles begin
to rise immediately from each electrode. - Clamp the first pair of test tubes and position them over
the electrodes, placed so that each tube catches the trail
of bubbles from one of the electrodes. - Note which tube is over the cathode of the battery and
which is over the anode. Use the marking pen to make a
minus sign on the tube over the cathode and a plus sign
on the tube over the anode.
As the reaction proceeds, you’ll notice that the gas in
one tube accumulates about twice as fast as the gas
in the other tube. When most of the water has been
displaced from one of the tubes, which may require 10
to 30 minutes, depending on the size of the test tubes,
insert a stopper into each of the two tubes while keeping
their mouths below the surface of the solution.
Unclamp the first set of tubes, remove them from the
beaker, rinse them with tap water, and place them in the
test tube rack.
Clamp the second set of tubes into position, and allow
gas to begin accumulating in them.
Remove the tube that was over the anode from the
rack. Strike a match, allow it to catch fire completely,
and then blow it out. While the burned end of the match
is still glowing, remove the stopper from the test tube
and thrust the glowing end of the match into the tube.
Record your observations on line A of Table 16-1.
Remove the tube that was over the cathode from the
rack. Strike a match, hold the burning match over the
mouth of the tube, and remove the stopper. Record your
observations on line B of Table 16-1.
Pour the solution that remains in the anode test tube
into the graduated cylinder, and record the volume of the
solution to 0.1 mL on line C of Table 16-1.
Pour the solution that remains in the cathode test tube
into the graduated cylinder, and record the volume of the
solution to 0.1 mL on line D of Table 16-1.
Fill one of the test tubes to the brim with water, and use
the graduated cylinder to measure the volume of water
the test tube contains when full. (You will probably have
to fill and empty the graduated cylinder two or three
times.) Record the volume of the test tube to 0.1 mL on
line E of Table 18–1.
Note the level of the gases in the second set of test tubes.
When the tube with the larger volume of gas has had
about two-thirds of the solution displaced by the gas,
reposition the test tubes so that the tube that was initially
over the anode is now over the cathode and vice versa.
Allow the reaction to proceed until both tubes are
nearly full of gas and the volume of gas in each tube is
about equal.
Stopper the tubes while keeping their mouths under the
surface of the solution.
Unclamp the second set of tubes, remove them from the
beaker, rinse them with tap water, and place them in the
test tube rack.