Question

What is the hydroxide ion concentration in a saturated solution formed by dissolving solid Zn(OH)₂ in pure water 25 C. K_sp od Zn(OH)₂ is 1.8 x 10^-14

Answer 1

Ksp of Zn(OH)2 = 1.8 x 10^-14

Zn(OH)2     -------------------> Zn²⁺ + 2 OH^-

                                                S          2S

Ksp = [Zn²⁺ ][OH-]^2

1.8 x 10^-14 = S x (2S)^2

1.8 x 10^-14 = 4S³

S = 1.65 x 10^-5 M

[OH-] = 2S = 2 x 1.65 x 10^-5

          = 3.3 x 10^-5 M

hydroxide ion concentration [OH-] = 3.3 x 10^-5 M