16.8 g of metallic cadmium is covered with 20 mL of water, which is then placed on a heating plate and heated to 60°C. A slow addition of 36.5 g of 65% nitric acid is started, after which the mixture is heated until no more nitrous fumes exhaust from the solution. The cadmium metal pieces are removed and the solution is poured into an evaporation dish, that is heated to about 100°C to remove water. Temperature control is mandatory, the residue can be dried in a desiccator to obtain a tetrahydrate.
Cd + 4 HNO3 = 2 NO2 + 2 H2O + Cd(NO3)2 ⋅ 4H2O
The cadmium metal immersed in water
Reaction taking place
The cadmium metal residue