question_answer 24)

What is the coordination entity formed when excess of aqueous KCN is added to an aqueous solution of copper sulphate? Why is it that no precipitate of copper sulphide is obtained when H2S(g) is passed through this solution?

Answer:

2CuSO4 (aq) + 10 KCN 2K3 [Cu(CN)4] +2K2SO4 + (CN)2 Thus, the co-ordination entity formed is [Cu(CN)4]3?. Since CN? is a strong ligand, the complex is stable. When H­2S is passed through this solution, no ppt. of Cu2S is formed because Cu ions are not lost when these are present in the co-ordination sphere.