AMMONIO-COPPER SULPHATE 227QUESTIONS- Treat 0.25 gram of the product with 5 cc. of hot 6N H 2 SO 4.
Note carefully the appearance of the undissolved residue, and
whether the solution is blue after the residue has settled. Read
the discussion of the preceding preparation and interpret the results
observed in this preparation. - Treat 0.25 gram of the product with 6 drops of water or
enough to moisten it and then add 6 N HCl a drop at a time noting
the progressive change in the appearance of the residue. Finally
see if a considerable amount (5-10 cc.) of the HCl will dissolve
the residue. Pour the clear solution into 500 cc. of cold water.
Read the discussion of the cuprous chloride preparation and
explain the observations made in this experiment. - Treat 0.25 gram of the product with 10 cc. of cold QN NH 4 0H
and compare the results with those of Experiment 2 under Cuprous
Chloride. Could you explain the difference by assuming that
cuprous oxide is much more insoluble than cuprous chloride in
pure water?
PREPARATION 30
AMMONIO-COPPER SULPHATE, CUSO4-4NH 3 -H 2 O
Preparation 3 illustrated the formation of a double salt, am-
monium copper sulphate, (NH^SOrCuSO^^O. In the double
salt, ammonium plays the part of a positive radical. In the
present preparation ammonia plays an altogether different role.
It does not possess a primary valence, and it enters into a molecular
compound with the salt by virtue only of a secondary valence.
In fact, the ammonia in this preparation is held in the same sort of
a combination as the water in the hydrate CuSO4-5H2O. The
molecules of ammonia would appear to be bound to the copper
rather than to the sulphate radical, because when the salt is dis-
solved in water the four ammonia molecules remain in combina-
tion with the copper as the complex ion Cu(NH 3 )4++, while the
sulphate radical appears as the ordinary SC>4~~ ion. Thus we
might say that this salt is the sulphate of the ammonio-copper
complex. (Cf. Ammoniates, page 118.)
The salt is exceedingly soluble in water, and therefore, in pre-
paring it, use is made of its insolubility in alcohol. The method
adopted of allowing the alcohol to mix with the aqueous solution