What is the pH?

Question

What is the pH of a saturated solution of Zn(OH)₂? (Ksp for Zn(OH)₂ = 3.0 × 10⁻¹⁶).

Answer 1

Zn(OH)₂(s) <==> Zn²⁺(aq) + 2OH^-(aq)

Ksp = [Zn²⁺][OH^-]²

3.0x10^-16 = (x)(2x)²

4x³ = 3.0x10^-16

x³ = 7.5x10^-17

x = 4.22x10^-6 = [Zn²⁺]

[OH^-] = 2 x 4.22x10^-6 = 8.44x10^-6 M

pOH = -log 8.44x10^-6 M

pOH = 5.07

pH = 14 - 5.07

pH = 8.93