A generic salt, AB3 , has a molar mass of 251 g/mol and a solubility of 1.10 g/L at 25 °C.

Question

What is the Ksp of this salt at 25 °C?

AB3(s)↽−−⇀A3+(aq)+3B−(aq)

Ksp= ?

Answer 1

Solubility in moles/liter = 1.10 g/L x 1 mol/251 g = 4.38x10^-3 M

AB₃(s) <==> A³⁺(aq) + 3B^-

[A³⁺] = 4.38x10^-3 M

[B^-] = 3 * 4.38x10^-3 M = 1.31x10^-2 M

Ksp = [A³⁺][B^-]³

Ksp = (4.38x10^-3)(1.31x10^-2)³ = (4.38x10^-3)(2.25x10^-6)

Ksp = 9.85x10^-9