238 HEAVY METALS OF GROUPS I AND IIresidue; let it run through the filter, and test the filtrate for
Ag+ ions by adding a drop of HC1. A distinct test is obtained.
Test a silver nitrate or a silver sulphate solution with litmus
and note that the indicator is not affected.The brown silver oxide must combine with water to form the
hydroxide when it dissolves because of the tests for Ag+ and OH~
ions that are obtained in the solution. Silver oxide is thus shown
to be appreciably soluble and markedly basic. As would be
expected of salts of such a base, we find that silver nitrate and
silver sulphate are not hydrolyzed. Silver oxide is exceptional for
a heavy metal oxide in displaying so marked a basic strength.
- Ammoniates. Repeat Experiments 3 using 6 N NH4OH
instead of NaOH. Note that in every case a limited amount of
reagent produces the same precipitate as NaOH, and that
excess of the reagent redissolves all the precipitates except
those of the mercury oxides.
Test the resulting ammonia silver salt solution for Ag+ ions
by adding a drop of KC1 and note that no precipitate is
formed.
The hydroxides dissolve in NH4OH, not because of any acidic
character but because of the ability of the metal ions to form
ammoniates (see pages 118-119). Addition of ammonia to the
simple metal radical seems to strengthen its metallic character so
that it can exist more easily as a positive ion. Thus the hydroxides
of the ammonio-metal radicals, excepting those of mercury, are
soluble and as highly ionized as the hydroxides of the alkali metals.
- Complex Negative Ions, (a) To 1 cc. 1N CuSO 4 add
10 cc. water and 2 cc. of 1N KI. Note that the solution turns
brown and that a precipitate is formed. Let the precipitate
settle, pour off the brown solution and note that a drop of it
will turn some starch paste blue, showing the presence of
iodine. Wash the precipitate by decantation and note that
it is white after the brown solution is removed. To the pre-
cipitate suspended in about 2 cc. of water add a small crystal
of potassium iodide. This dissolves quickly, giving a fairly
concentrated solution. Note that the precipitate dissolves
in the KI solution.