Synthetic Inorganic Chemistry

90 THE THEORY OF IONIZATION

add some ammonium chloride solution. Explain the effect on the

hydroxyl-ion concentration of adding an ammonium salt to an

ammonium hydroxide solution.

(d) To 1 cc. of a ferric chloride solution add 5 cc. of water and

then a few drops of ammonium hydroxide solution. Then add

some ammonium chloride solution.

CHARACTERISTIC REACTIONS OF CERTAIN IONS
If two ionized substances are brought together in a solution,
and one of the possible new combinations of a positive and a
negative ion is an insoluble solid substance, that substance will
form as a precipitate. Characteristic precipitates serve as a
means of identifying specific ions.
Some ions possess characteristic colors which they impart to a
clear solution. Thus the cupric ion, CU++, is blue and all dilute
solutions of cupric salts are clear blue unless the color is modified by
another colored component. Thus the appearance of a color or
a change of color in a clear solution when a reagent is added helps
to identify the ions present.
In the following experiments an inexperienced student always
is impelled to make the mistake of using too concentrated solu-
tions and adding too much reagent. This not only wastes ex-
pensive chemicals, but it also obscures the effects to be observed.
The procedure that should be followed is to take about 1 cc. of
the solution to be tested, dilute this with 5 cc. of water, and add
the reagent a single drop at a time, shaking thoroughly after each
drop. In this way keep adding reagent until no further change
is brought about. It often happens that a limited amount of
reagent will produce an effect, say a precipitate, and a larger
amount will produce another effect, say redissolve the precipitate.
If the reagent is "dumped in " carelessly these effects maybe missed.

12. Chloride Ions. To solutions of various chlorides, such as
    hydrochloric acid, sodium chloride, and calcium chloride, add a few
    drops of a solution of a silver salt — silver nitrate or silver sul-
    phate. To the resulting suspension add 6 N HN0 3. Does the
    precipitate dissolve?
    To a solution of potassium chlorate (free from chloride) add a
    few drops of silver nitrate.
    How may the presence of chloride ions be recognized? Why
    is not the same test given by the chlorine in potassium chlorate?