Answer to Question #112686 in General Chemistry for Beverlie

Question

1. Calculate the solubility (in M) of cobalt(II) hydroxide, Co(OH)2(s) in H2O. Ksp = 3.60×10-16 at a specific temperature.
2. What is the pH of this solution of cobalt(II) hydroxide?

Answer 1

Solution.

$Co(OH)_2 \iff Co^2$ ⁺ $+ 2OH^-$ ;

x 2x

$K_sp = \lbrack Co^2+\rbrack\lbrack OH^-\rbrack^2 =x(2x)^2 = 4x^3 =3.6\sdot10$^-16;

$x^3 = 0.9\sdot10$ ^-16;

$x = 0.45\sdot10$ ^-5;

The molar solubility is 0.45$\sdot$ 10^-5 mol/L;

pH of Co(OH)2 pH=9.15;

Answer: The molar solubility is 0.45⋅ 10^-5 mol/L; pH = 9.15.