A generic salt, AB2, has a molar mass of 249 g/mol and a solubility of 1.10 g/L at 25 °C. What is the Ksp of this salt at 25 °C?

Solubility = 1.10 g/L = (1.10 g/L) / (249 g/mol) = 0.00442 M

The equation for the solubilizing of AB₂ :
____________ AB₂(s) __ ⇌ __ A⁺(aq) __ + __ 2B⁻(aq) ___ Ksp
Initial: ___________________ 0 M _________ 0 M
Change: ______________ +0.00442 M __ +2×0.00442 M
At eqm: _______________ 0.00442 M ___ 0.00884 M


Ksp = [A⁺] [B⁻] = 0.00442 × 0.00884² = 3.45 × 10⁻⁷

Ksp .....

AB2(s) <==> A(aq) + 2B(aq) .............. Ksp = ???

solubility = 1.10 g/L
molar mass = 249 g/mol
concentration = (1.10g / 1L) x (1 mol / 249g) = 0.00442 mol/L

[A^2+] = 0.00442 mol/L
[B^-] = 0.00884 mol/L

Ksp = [A^2+][B-]²
Ksp = 0.00442 x (0.00884)²
Ksp = 3.45x10^-7