Calculate the solubility at 25 °C of Co(OH)2 in pure water and in a 0.0130M CoCl2 solution.

Question

Calculate the solubility at 25 °C of Co(OH)2 in pure water and in a 0.0130M CoCl2 solution.

Co(OH)₂ K_sp = 5.92 x 10^-15

Round both of your answers to 2 significant digits.

solubility in pure water: ______g/L

solubility in 0.0130M CoCl2 solution: ______g/L

Answer 1

One would have hoped that after several of these problems being done, you might be able to do them yourself. What is the problem? What don't you understand?

Co(OH)₂(s) <==> Co²⁺(aq) + 2OH^-(aq)

Ksp = [Co²⁺][OH^-]² let x = [Co²⁺] and 2x = [OH^-]

5.92x10^-15 = (x)(2x)² = 4x³

x³ = 1.48x10^-15

x = 1.14x10^-5 M = 1.1x10^-5 M = solubility in pure water

Common ion is Co²⁺ which comes from 0.0130 M CoCl₂. We can ignore the Co²⁺ from the Co(OH)₂ as it is only 1.1x10^-5 M.

Ksp = [Co²⁺][OH^-]²

5.92x10^-15 = [0.0130][OH-]²

[OH-]² = 4.55x10^-13

[OH-] = 6.75x10^-7 M

[Co(OH)₂] = 1/2 x 6.75x10^-7 M = 3.4x10^-7 M = solubility in 0.0130 M CoCl₂