Nickel Dichloride, NiCl₂

Nickelous Chloride or Nickel Dichloride, NiCl₂, is prepared in the anhydrous condition by heating the finely divided metal in dry chlorine. It may also be obtained by evaporating to dryness a solution of nickel oxide (or carbonate) in aqueous hydrogen chloride, and heating gently the solid residue in the absence of air, most advantageously in dry hydrogen chloride gas. The salt sublimes as golden scales of density 2.56.

When heated in air nickel chloride decomposes, evolving chlorine and leaving the oxide. At dull red heat in dry hydrogen a volatile compound, possibly NiClH, is produced. Upon exposure to air the scales absorb moisture and then become easily soluble in water. From such solutions the hexahydrated salt, NiCl₂.6H₂O, is obtained upon evaporation. When exposed to ammonia the anhydrous salt swells to a white powder of formula NiCl₂.6NH₃, readily soluble in water. A substance of similar empirical composition may be obtained as blue octahedra by dissolving nickel chloride in concentrated ammonia, and either allowing to cool or by addition of alcohol. It evolves ammonia upon exposure to air, and particularly in vacuo.

Nickel chloride is also soluble in alcohol.

Several hydrates are known. The monohydrate, NiCl₂.H₂O, is obtained as a yellowish green salt on adding hydrochloric acid to a solution of the chloride in water. The dihydrate, NiCl₂.2H₂O, results upon keeping the hexahydrate in a desiccator. It is yellow in colour.

The usual form of the salt is the hexahydrate, NiCl₂.6H₂O, which may most easily be obtained by dissolving one of the oxides or the carbonate of nickel in hydrochloric acid and crystallising out. It yields monoclinic prisms isomorphous with the corresponding cobalt salt. It is deliquescent, and soluble both in water and alcohol.

The solubility of nickel chloride in water is as follows:

Temperature ° С	0	10	20	40	60	100
Grams NiCl2 per 100 grams solution.	35.0	37.3	39.1	42.3	45.1	46.7

When exposed to hydrogen under a pressure of 100 atmospheres at 250° C., a fifth normal solution of nickel chloride deposits a little metallic nickel.