Calculate the concentration of chloride ions in a saturated lead

PbCl2 (s) Pb2 + (aq) + 2 Cl - (aq)

for which the equilibrium requirement is

Ksp = [Pb2+][Cl-]^2

Let x = mol/L PbCl2 that dissolves to estabilish equilibrium.

This will produce x mol/L Pb2 + and 2x mol/L Cl-

This gives us at equilibrium:

[Pb2+] = x and [Cl-] = 2x = 6.2 x 10^-4 mol/L

x = [Pb2+] = 6.2 x 10^-4 / 2 = 3.1 x 10^-4 mol/L

Ksp = (3.1 x 10^-4) (6.2 x 10^-4) ^2 = 1.2 x 10^-10