Zinc Nitrate, Zn(NO₃)₂

The anhydrous salt may be prepared by dehydrating the hydrated salt at 130°-135° C. in an atmosphere of nitrogen pentoxide. The pasty mass crystallises on cooling and dissolves in water with great evolution of heat. According to Pierre, the hexahydrate loses all its water at 105° C. in a current of dry air.

From solutions of zinc nitrate obtained by ordinary methods, the hexahydrate, Zn(NO₃)₂.6H₂O, crystallises at ordinary temperatures in transparent four-sided prisms. It is deliquescent, has a density of 2.063 at 13° C. and 2.067 at 15° C., melts at 36.4° C., and is very soluble both in water and alcohol.

Its solubility varies from 44.63 parts of Zn(NO₃)₂ in every 100 parts of solution at -18° C. to 63.63 parts at +36° C.

It loses half of its water at 100° C., but prolonged heating results in the formation of basic salts, and if the heating is conducted in vacuo a mixture of zinc oxide and the trihydrate appears to remain. It boils at 131° C., and remains clear till it loses 42 per cent, of its weight. The glassy mass then cools to crystalline 3Zn(NO₃)₂.ZnO.3H₂O. At higher temperatures it is completely converted into zinc oxide.

On prolonged desiccation over sulphuric acid it loses half of its water and some nitric acid, a basic salt being left. Its heat of solution is -5.840 Cal.

Between 34° C. and 36.4° C. it is transformed into the trihydrate, which crystallises in small needles when the hexahydrate is kept molten for some time at 37°-40° C., or when a solution of zinc nitrate, containing a little sulphuric acid, is concentrated on the water-bath and allowed to stand over sulphuric acid. The needles melt at 45.5° C. and quickly become the hexahydrate in the air. The solubility of the trihydrate varies from 66.38 parts of anhydrous salt in every 100 parts of solution at 37° C. to 77.77 parts at 45.5° C.

Zinc nitrate crystallises from its solutions at temperatures below about -17.5° C. as the nonahydrate. This is most easily obtained by cautiously melting the cryohydrate formed at - 29° C. Its solubility Varies from 40.12 parts of anhydrous salt in 100 parts of solution at -25° C. to 43.59 parts at -18° C.