Nickel Nitrate, Ni(NO₃)₂

Nickelous Nitrate or Nickel Nitrate, Ni(NO₃)₂ may be obtained in the anhydrous condition by the action of nitric anhydride or a solution of this in nitric acid upon the hydrated salt. It is a pale greenish yellow powder, which decomposes at 105° to 110° C., evolving nitrous fumes.

The hexahydrate, Ni(NO₃)₂.6H₂O, is dimorphous. It is obtained as green monoclinic crystals by concentration of a solution of nickel hydroxide or carbonate in dilute nitric acid at temperatures below 55° C. - most advantageously at about 40° C. Density 2.065 at 14° C. At low temperatures the salt separates out in crystalline lamellae. The crystals deliquesce in moist air and effloresce in the dry. Their solubility in water is as follows:

Temperature ° C	-21	-12.5	-10	-6	0	20	41	56.7
Grams Ni(NO3)2 per 100 grams solution.	39.94	41.59	42.11	43.00	44.32	49.06	55.22	62.76

The composition of a saturated solution of the hexahydrate in water at temperatures ranging from -21° to 41° C. is given by the expression:

Ni(NO₃)₂ + (12.886 - 0.11355t)H₂O.

Crystals of the hexahydrate melt at about 56.7° C., losing 3 molecules of water. If maintained at 70° C. they melt, large orthorhombic crystals of the trihydrate, Ni(NO₃)₂.3H₂O, being produced. This hydrate is stable between c. 55° and 95° C., at which latter temperature the crystals melt with simultaneous decomposition.

The solubility of the trihydrate in water is as follows:

Temperature ° C.	58	60	64	70	90	95
Grams Ni(NO3)2 per 100 grams solution.	61.61	61.99	62.76	63.95	70.16	77.12

At 55° C. nickel nitrate has nearly the same solubility as the corresponding cobalt salt.

At -16° C. the nonahydrate, Ni(NO₃)₂.9H₂O, can be isolated from the solution, but only with difficulty on account of the low temperature. Its solubility in water is as follows:

Temperature ° C.	-23	-21	-10.5
Grams Ni(NO3)2 per 100 grams solution	39.02	39.48	44.13

The solubility curve of this hydrate intersects that of the hexahydrate at -16° C.

When alcohol is added to a solution of nickel nitrate in aqueous ammonia, blue octahedral crystals of the monohydrated tetrammoniate, Ni(NO₃)₂.4NH₃.H₂O, separate out. These are unstable in air.

A double nitrate of nickel and bismuth, 3Ni(NO₃)₂.2Bi(NO₃)₃.24H₂O, has been prepared as green crystals, melting at 69° C. without decomposition. Other double nitrates are known, including double nitrates of certain rare earth metals, and several basic salts had been prepared.