The maximum pH of a solution which is 0.1 M in Mg2+ from which Mg(OH)2 is not precipitated is

Q: The maximum pH of a solution which is 0.1 M in Mg2+ from which Mg(OH)2 is not precipitated is

(A) 4.96

(B) 6.96

(C) 7.54

(D) 9.04

Given that Ksp for Mg(OH)2 = 1.2 × 10–11

Solution: $\large Mg(OH)_2 \rightleftharpoons Mg^{2+} + 2 OH^-$

Ksp = [Mg2+][OH]2

1.2 × 10–11 = 0.1 × [OH]2

[OH] = 1.1 × 10-5

$\large [H^+] = \frac{10^{-14}}{1.1 \times 10^{-5}}$

= 9.09 × 10-10 M

pH = -log (9.09 × 10-10)

= 10 – 0.9586 = 9.04