Synthetic Inorganic Chemistry

AMMONIUM-COPPER SULPHATE 61

PREPARATION 3
PREPARATION OF A HYDRATED DOUBLE SALT
AMMONIUM-COPPER SULPHATE, (NH 4 ) 2 SO 4 -CUSO 4 -6H 2 O
Besides forming molecular compounds with water (hydrates)
certain salts have the property of combining with a second salt
either with or without water. In these combinations the charac-
ter of the individual salts is somewhat modified but not completely
changed. Hence the name, " double salts". In physical prop-
erties such as crystalline form, solubility, and, in some cases, color,
the crystals of the double salt differ from those of the simple salts.
These compounds follow the law of definite proportions.

Ammonium sulphate crystallizes from solution as the anhydrous
salt, (NH 4 )2SO 4 ; copper sulphate as the hydrate, CuSO 4 -5H 2 O;
but when equivalent amounts of the two salts are in solution
together the double salt, (NH 4 ) 2 SO 4 -CuSO 4 -6H 2 O, separates first
because it is less soluble than either of the single salts.

Materials: copper sulphate, CuSO 4 -5H 2 O, 50 grams = 0.2 F.W.

ammonium sulphate, (NH 4 ) 2 SO 4 , 27 grams = 0.2

F.W.

Apparatus: 8-inch porcelain dish.

8-inch crystallizing dish.

5-inch funnel and filter paper,

iron ring and ring stand.

Bunsen burner.

Procedure: Pulverize the copper sulphate, and dissolve it with

the ammonium sulphate in 250 cc. of warm water, to which 10 drops

of 6 N H 2 SO 4 have been added. The solution should not be boiled.

Filter the warm solution into an 8-inch crystallizing dish covered

with a glass plate except where the stem of the funnel enters, and

allow it to stand over night with the cover on. Remove the cover

and allow water to evaporate slowly until a satisfactory yield has

been obtained. This usually requires about 4 days. Seed crystals

are available at the store room, but crystallization usually starts as

soon as the solution cools to room temperature. If a crystal meal

is desired follow the procedure suggested in Note 8 (a), page 14.

Decant the mother liquor from the crystals, wash them with a

little distilled water, and dry them thoroughly, at room tempera-