Question

At a certain temperature, the solubility of strontium arsenate, Sr3(AsO4)2, is 0.0520 g/L. What is the Ksp of this salt at this temperature?

Answer 1

Molar mass of Sr₃(AsO₄)₂ = 540.6984 g/mol

Solubility of strontium arsenate (S) = 0.0520 g/L

                                                        = 0.0520/ 540.6984 mol/L

                                                        = 9.62 x 10^-5 M

                                                          Sr₃(AsO₄)₂ $\rightleftharpoons$ 3 Sr²⁺ + 2 AsO₄^3-

Equilibrium concentration (M):                                    3S             2S

Now,

K_sp = [Sr²⁺]³[AsO₄^3-]²

       = (3S)³(2S)²

       = (27S³)(4S²)

       = 108S⁵

       = 108 x (9.62 x 10^-5)⁵

       = 8.89 x 10^-19

Therefore, K_sp of this salt at this temperature = 8.89 x 10^-19