Question

The solubility of PbI₂ (K_sp = 9.8 x 10^-9) varies with the composition of the solvent in which it was dissolved. In which sol­vent mixture would PbI₂ have the lowest solubility at identical temperatures?

            a.         pure water                   b.         1.0 M Pb(NO3)2(aq)

            c.         1.5 M KI(aq)             d.         0.8 M MgI₂(aq)

            e.         1.0 M HCl(aq)

Answer 1

Ans :-

Solubility of sparingly soluble salt always decreases in the presence of common ion. Since, MgI2 contains 2 moles common ions i.e. Iodine whose concentration is 2 x 0.8 M = 1.6 M. On the other hand KI contains onle 1 mole of common ion i.e. iodine whose concentration = 1.5 M. Therefore, solubility of PbI2 will be lowest in 0.8 M MgI2.

So, Option (d) is the answer.