Question

Calcium oxalate (CaC2O4) has a Ksp value of 2.3 × 10–9 at 25°C. Calculate the molar solubility of Ca2+ and C2O42– in one liter of aqueous solution.
Ksp = [X] × [X]

What is the molar solubility of Ca2+?

2.3 x 10-9 M

4.8 x 10–5 M

4.60 x 10-9 M

5.29 x 10-18 M

Answer 1

Ksp is the equilibrium constant of solubility of a solid in a solution.

The solid is CaC2O4.

The dissolved ions are Ca2+ and C2O4 2-

The equation of the equilibrium is
$CaC_{2}O_{4} = Ca^{2+} + {C_{2}O_{4}}^{2-}$

Then Ksp = [Ca 2+][C2O4 2-]

Where the [ ] indicates molar concentration

The chemical equation for this equilibrium implies [Ca 2+] = [C2O4 2-]. Name X this quantity

Ksp = x^2 ==> x = square root of Ksp

x = sqrt(2.3 * 10^ -9) = 4.8 * 10^ -5

Which is the second option.