Cupric nitrate, Cu(NO₃)₂

Crystallization of a solution of cupric oxide or carbonate in dilute nitric acid yields the nitrate in the form of deliquescent hydrates. Below –20.5° C. the nonahydrate crystallizes; below 24.5° C. the hexahydrate in blue, tabular crystals; and above this temperature the trihydrate in prismatic, columnar crystals, m.p. 114.5° C., density 2.047. The anhydrous salt is prepared by treating the dried powder with nitric acid containing excess of nitric anhydride, and drying the residue over calcium oxide and phosphoric oxide. It is a white, deliquescent substance, which begins to decompose at 155° to 160° C. At red heat it is converted into cupric oxide. At 8° C. its heat of solution is 10.47 Cal. The heat of formation of the anhydrous salt from its elements is 71.49 Cal.; that in solution is 81.96 Cal. Thomsen's value for the heat of formation of the hexahydrate from the anhydrous salt and liquid water is 21-18 Cal., and from its elements and water 92.94 Cal. It yields a green, basic salt, Cu(NO₃)₂,3Cu(OH)₂. A complex ammonia derivative, Cu(NO₃)₂,7NH₃, is formed in pale-blue crystals by the action of reduced copper on silver nitrate in presence of liquid ammonia. In vacuum over sulphuric acid it changes to pale-violet crystals, Cu(NO₃)₂,4NH₃.