232 DIY Science: Illustrated Guide to Home Chemistry Experiments
FIGURE 13-1: Saturated sodium chloride solutions with (from left
to right) hydrochloric acid, sodium carbonate, magnesium sulfate,
and water added
adding sodium carbonate until some of it remains
undissolved at the bottom of the test tube.- Prepare a saturated solution of magnesium sulfate by
adding about 1.3 g of magnesium sulfate to 5 mL of water
in a test tube. Stir or shake the solution to ensure that the
magnesium sulfate dissolves completely, and continue
adding magnesium sulfate until some of it remains
undissolved at the bottom of the test tube. - Prepare a saturated solution of sodium chloride by adding
about 40 g of sodium chloride to 100 mL of water in a
small beaker or flask. Stir or shake the solution to ensure
that the sodium chloride dissolves completely, and
continue adding sodium chloride until some of it remains
undissolved at the bottom of the beaker or flask. - Transfer about 5.0 mL of the saturated sodium chloride
solution to each of four test tubes, labeled A through D,
one of which will serve as the control. The exact amount
of solution is not critical, but make sure that each test
tube contains the same amount. - Place the test tubes adjacent to each other in a test tube
rack under a strong light. (It may be easier to observe the
reactions if you place a sheet of black construction paper
or a similar material behind the test tube rack.) - Add concentrated hydrochloric acid dropwise to test
tube A, observing any change that occurs as each drop is
added. Continue adding hydrochloric acid until you have
added about 5 mL. - Add saturated sodium carbonate solution dropwise to
test tube B, observing any change that occurs as each
drop is added. Continue adding the saturated sodium
carbonate solution until you have added about 5 mL. - Add saturated magnesium sulfate solution dropwise to
test tube C, observing any change that occurs as each
drop is added. Continue adding the saturated magnesium
sulfate solution until you have added about 5 mL.
Add water dropwise to test tube D, the control test tube,
observing any change that occurs as each drop is added.
Continue adding water until you have added about 5 mL.
PRTII: A
ExAmINE THE EffECT of TEmpERATURE oN EqUILIBRIUm
In our saturated solution of sodium chloride, solid sodium
chloride exists in equilibrium with aqueous sodium ions and
chloride ions. Le Chatelier’s Principle tells us that changing the
temperature of the reaction environment will cause a change
in that dynamic chemical equilibrium, but we have no way of
knowing the direction of that change. Intuitively, we expect that
more sodium chloride will dissolve in a given volume of water at a
higher temperature, so let’s test that hypothesis:- If you have not already done so, put on your splash
goggles, gloves, and protective clothing. - Transfer about half of the remaining saturated sodium
chloride solution (~40 mL) to a small beaker or flask. - Add a small amount of sodium chloride to the beaker or
flask; just enough so that undissolved sodium chloride
crystals are visible on the bottom of the beaker or flask. - Set up your tripod stand, wire gauze, and alcohol burner.
- With stirring, gently heat the beaker or flask that contains
the saturated sodium chloride solution, keeping an eye on
the undissolved sodium chloride.
10.
PRTIII: A
ExNEAmI THE EffECT of voLUmE oN EqUILIBRIUm
In our saturated solution of sodium chloride, solid sodium
chloride exists in equilibrium with aqueous sodium ions and
chloride ions. Le Chatelier’s Principle tells us that changing
the volume of the solvent will cause a change in that dynamic
chemical equilibrium. Intuitively, we expect that if X g of sodium
chloride dissolves in Y mL of water, increasing the amount of
water will increase the amount of sodium chloride that dissolves.
Let’s test that hypothesis:- If you have not already done so, put on your splash
goggles, gloves, and protective clothing. - Make sure that the remaining saturated sodium chloride
solution (~40 mL) has some undissolved sodium chloride
visible in the bottom of the beaker or flask. Note the
approximate amount of undissolved sodium chloride. - Add 10 drops of water to the beaker or flask, and stir or
swirl the solution to determine whether any additional
sodium chloride dissolves. - Continue adding water 10 drops at a time until all of the
visible undissolved sodium chloride has dissolved.
PIRTA v:ExNEAmI THE EffECT of pRESSURE
(ANd TEmpERATURE) oN EqUILIBRIUm
Le Chatelier’s Principle says that changing the pressure of
the reaction environment will change the dynamic chemical
equilibrium. Carbonated soft drinks contain dissolved carbon
dioxide gas, which is more soluble at higher pressures. If
we reduce the pressure, we expect the soft drink solution