Solubility Products

Question

What is the molar solubility (in mol/L) of PbCl₂ (Ksp = 4.18⋅10^−13) in a 0.16 M NaCl solution. 

Answer 1

Common Ion Effect:

The common ion in this problem is Cl^- which comes from PbCl₂ and from NaCl

[Cl-] = 0.16 M (the contribution of Cl^- from PbCl2 is small compared to that from NaCl and is ignored.

PbCl₂(s) <==> Pb²⁺(aq) + 2Cl^-(aq)

Ksp = 4.18x10^-13 = [Pb²⁺][Cl^-]²

4.18x10^-13 = (x)(0.16)²

4.18x10^-13 = 0.0256x

x = 1.63x10^-11 M = solubility of PbCl₂ in 0.16 M NaCl