DISPLACEMENT OF WEAK ACIDS AND BASES 89
whether it has an odor. Add a few drops of 6 N H 2 SO 4 to the warm
sodium acetate solution and observe whether there is an odor of
acetic acid. Suppose that exactly equal volumes of 0.2 N
NaC 2 H 3 O 2 + 0.2N HC1 had been used; what percentage of the
way to completion would the reaction have gone? Compare the
completeness of this reaction with that of neutralization.
(c) To 5 cc. of sodium carbonate solution add acetic acid, a
few drops at a time, till action ceases. What is the gas formed?
What acid is displaced in this case? How is the completeness of
its displacement affected by the escape of the gas?
(d) Treat a small quantity of calcium carbonate with an excess
of dilute hydrochloric acid, and see whether it will all dissolve.
Calcium carbonate is usually considered as an insoluble substance,
nevertheless it is slightly soluble in pure water. Look up its
exact solubility (solubility table on page 364). How would the
acid react with the small amount of calcium carbonate in solution?
How would the equilibrium between the solid calcium carbonate
and its saturated solution be affected by this reaction? To sum
up, explain how the calcium carbonate dissolves in acids.
- Displacement of a Weak Base from Its Neutral Salt by
Means of a Stronger Base, (a) Note whether a solution of am-
monium chloride has the odor of ammonia. Warm 2 cc. of this
solution to about 50°, note again whether there is an odor; add a
little sodium hydroxide solution and again note if there is an odor.
At 50°, ammonia, NH 3 , from the non-electrolytic dissociation
of NH 4 0H (see page 111), escapes as a gas from the solution to a
sufficient extent to give a powerful odor. Thus the odor of am-
monia indicates the presence of NH4OH in solution. On the other
hand, the amount of gas which escapes during this experiment is
too small to cause a significant change of concentration of the com-
ponents of the solution. If equal volumes of cold 0.2 N NH 4 C1
and 0.2 N NaOH are mixed, to what degree of completion does the
formation of un-ionized NH4OH proceed?
(6) To 1 cc. of a magnesium sulphate solution add 5 cc. of water
and then a few drops of sodium hydroxide solution. Look up
the solubility and the degree of ionization of magnesium hydroxide
(page 101). Calculate the hydroxyl-ion concentration in a sat-
urated solution of Mg(0H) 2.
(c) To 1 cc. of magnesium sulphate solution add 5 cc. of water
and then a few drops of ammonium hydroxide solution. Then
