Question

1) Calculate the metal cation concentration of the following sparingly soluble salts in a 0.0167 M solution of Mg(ClO4)2 using activities:

(a) SnI2 (Ksp = 8.3 x 10¯6)

(b) PbSO4 (Ksp = 6.3 x 10¯7)

Answer 1

From the given information, reaction occur in 1st case

Mg(ClO4)₂ + SnI₂ ------------> Sn(ClO4)₂ + MgI₂

Mg(ClO4)₂ = 0.0167 M

K_sp = 8.3 X 10^-6

0.0167 M Mg(ClO4)₂

K_sp of Mg(ClO4)₂= 49.6 from solublity table

(ClO4)₂ = 0.0167 / 49.6 = 3.37 X 10^-4 M

Mg²⁺ = 0.0167 / 49.6 = 3.37 X 10^-4 M
Ionic product of Sn(ClO4)₂ = [Sn²⁺ ][(ClO4)₂]

K_sp = [Sn²⁺ ][(ClO4)₂]
8.3 x 10^-6 = [Sn²⁺ ] X 3.37 X 10^-4

[Sn²⁺ ] = 8.3 x 10^-6/3.37 X 10^-4

[Sn²⁺ ] = 2.46 X 10^-2 M

For Second solution PbSO4 (Ksp = 6.3 x 10^-7)

Mg(ClO4)₂ + PbSO₄ ------------> Pb(ClO4)₂ + MgSO₄

Ionic product of Sn(ClO4)₂ = [Pb²⁺ ][(ClO4)₂]

K_sp = [Pb²⁺][(ClO4)₂]
6.3 x 10^-7 = [Pb²⁺] X 3.37 X 10^-4

[Pb²⁺] = 6.3 x 10^-7/3.37 X 10^-4

[Pb²⁺] = 0.0187 X 10^-3 M

[Pb²⁺] = 1.87 X 10^-5 M