CHARACTERISTIC REACTIONS OF CERTAIN IONS 91- Sulphate Ions. To solutions of soluble sulphates, such as
sodium sulphate, copper sulphate, sulphuric acid, add barium
chloride solution. After the effect of this reagent is noted add
hydrochloric acid to see whether the precipitate is redissolved by
acid. - Copper Ions, (a) To 5 cc. of copper sulphate solution,
add NH 4 OH in small amount and then in excess.
In writing ionic equations consider the light blue precipitate as
Cu(OH) 2 , for the sake of simplicity, instead of the rather indefinite
basic salt. To explain the deep blue color consult page 118.
(b) To another sample of cupric salt solution add ammonium
sulphide. Divide the black suspension in two parts; add HC1
to one part, and NH 4 OH to the other, to see whether the precipi-
tate is soluble in either of these reagents. - Zinc Ions. Repeat every step of the preceding experiment
using a zinc salt instead of a copper salt.
Using the information gained in these two experiments, devise
a method by which you could detect the presence of a small amount
of zinc salt in a solution containing copper salt. - Ferrous Ions. Repeat (a) and (6) of Experiment 14 upon a
ferrous salt instead of a cupric salt.
(c) To a solution of ferrous sulphate add a freshly prepared
solution of potassium ferricyanide, K3(Fe(CN) 6 ). - Ferric Ions, (a) To a solution of ferric chloride add
NH4OH.
(6) To other samples of the ferric salt solution add potassium
ferrocyanide K 4 (Fe(CN) 6 ), and potassium thiocyanate, KCNS,
respectively. - Silver Ions, (a) Recalling Experiment 12, state how
chloride ions may be used as a reagent for silver ions.
(6) To 2 cc. of 0.1 N AgNO 3 add NH 4 0H very cautiously as
follows so as to avoid an excess at the beginning. Dilute 1 cc.
of the 6iV NH4OH with 10 cc. of water, and transfer 1 drop of
the dilute solution, hanging to the end of a stirring rod, to the
AgNC>3 solution. Continuing to add the reagent in these very
small portions, observe whether a precipitate is formed at any time,
and-whether it redissolves with an excess of the reagent.
(c) To 2 cc. of 0.1 N AgNO 3 add 0.5 cc. of liV NaCl, which
gives an excess of chloride ions.
Add 6 N NH4OH cautiously so as to avoid a large excess until