Equilibrium and solubility product

Question

In which of the following will PbBr2(s) be least soluble?

 

pure water

0.01M NaBr

0.01M KBr

0.02M NaBr

PbBr2 will be equally soluble in all of the above solutions

Answer 1

It will be least soluble in 0.02 M NaBr because of the common ion effect, Br being the common ion.

PbBr₂ ==> Pb²⁺ + 2Br^-

Ksp = [Pb²⁺][Br^-]²

In 0.02 M NaBr, the [Br] is greater than in any of the other solutions, so the value of [Pb^2+] x [Br^-]² will exceed the Ksp by more than the others.