Determine the molar solubility (S) of Zn(CN)2

Question

Determine the molar solubility (S) of Zn(CN)2 in a solution with a pH= 5.53. Ignore activities. The Ksp for Zn(CN)2 is 3.0 x 10^-16. The Ka for HCN is 6.2 x 10^10.

please help thank you!

Answer 1

Common ion effect.

Zn(CN)2(s) <==> Zn²⁺(aq) + 2CN^-(aq)

Ksp = [Zn²⁺][CN^-]²

Since pH is given (5.53), we can determine the [CN^-], which is a common ion as it is also present in Zn(CN)₂.

HCN ==> H⁺ + CN^-

[H⁺] = 1x10^-5.53 = 2.95x10^-6 = [CN^-]

Ksp = [Zn²⁺][CN^-]²

3.0x10^-16 = (s)(2.95x10^-6)²

3.0x10^-16 = (s)(8.70x10^-12)

s = 3.45x10^-5 M = solubility of Zn(CN)₂