Question

The coordination entity formed when excess of KCN is added to an aqueous solution of CuSO₄ is

(a) [Cu(CN)2]⁺

(b) [Cu(CN)₆]^4-

(c) [Cu(CN)₄]^2-

(d) [Cu(CN)₄]³⁺

Answer 1

Answer is (c) [Cu(CN)₄]^2-

[Cu(CN)₄]^2- is stable complex having

k = 2 x 10²⁷. It does not provide

sufficient Cu²⁺ ion to give precipitate of CuS.