Three separate solutions are prepared by dissolving 100 g of copper sulfate pentahydrate in 1 L of hot water, 15 g of sodium hydroxide in 90 mL of cold water and 28.41 g of potassium ferrocyanide trihydrate and 19.8 g of sodium metabisulphite in 400 mL of water. The hydroxide and ferrocyanide solutions are combined and added to the sulfate solution with stirring, the pH of the solution needs to be maintained at pH 5.5 with NaOH. The suspension is stirred for 1 h and left to cool overnight, the mixture is then filtered and washed with water. The product may be dried in open air.
6 CuSO4 + K4[Fe(CN)6 + 3 SO2 + 6 H2O = CuCN + K2SO4 + FeSO4 + 6 H2SO4
The reaction taking a place
The mixture after the reaction is complete