Nickel Perchlorate, Ni(ClO₄)₂

Nickel Perchlorate, Ni(ClO₄)₂, may be obtained by dissolving nickel hydroxide or carbonate in a solution of perchloric acid, expelling the excess of acid at 110° C., and concentrating to crystallisation. The salt separates out in long, green needles, soluble in water, alcohol, and acetone, but insoluble in chloroform. The salt may be dried by warming in a current of dry air or by prolonged exposure over sulphuric acid. It then has the formula Ni(ClO₄)₂.5H₂O. The crystals melt at 149° C., but already at 103° C. slight decomposition sets in with loss of perchloric acid and production of basic salt. The solution in water gradually undergoes hydrolytic dissociation, nickel hydroxide being precipitated.

If a piece of blotting or filter paper is moistened with a solution of nickel perchlorate and introduced into the tip of a Bunsen flame, a series of small detonations ensues.

At -21.3° C. the nonahydrate, Ni(ClO₄)₂.9H₂O, is formed.

Two other hydrates, namely, the hexahydrate, Ni(ClO₄)₂.6H₂O, and the tetrahydrate, Ni(ClO₄)₂.4H₂O, have been described, as also the hexammoniate, Ni(ClO₄)₂.6NH₃.

The solubility of nickel perchlorate in water is as follows:

Temperature °C,	-30.7	-21.3	0	7.5	18	26	45
Grams Ni(ClO4)2 in 100 grams of solution.	20.505	21.06	23.55	24.32	25.06	25.55	27.02
Density of solution.			1.5726	1.5755	1.5760	1.5841	1.5936

The anhydrous salt apparently cannot exist since the hydrated salt decomposes on warming before all the water has been expelled.