Question

Ksp for copper (II) hydroxide, Cu(OH)2, is 2.2x10-20 at 25°C. Calculate the molar (in mol/L) and gram solubility (in g/L) of copper (II) hydroxide. (Report your answers in scientific notation.) Molar solubility = Preview mol/L Gram soubility = Preview

Answer 1

Given that,

K_sp = 2.2 x 10^-20

Temperature = 25⁰C

Let us consider a reaction,

Cu(OH)₂$\rightleftharpoons$ Cu²⁺ + 2OH^-

Ksp = [Cu²⁺] [OH^-]²

Let solubility be S

2.2$\times$10^-20  = S $\times$ (2S)²

= S $\times$ 4S²

= 4S³

S³ = 2.2$\times$10^-20 / 4

S = 1.76 $\times$10^-7

The molar solubility of Cu(OH)₂  = 1.76 $\times$10^-7 mol/L

The gram solubility of  Cu(OH)₂ = Solubility x Molar mass   

= 1.76 $\times$10^-7 x 98 g / mol

= 1.7 $\times$10^-5 g/L