What is the equilibrium concentration of Ca2+ in a saturated solution of CaCrO4?

**Answer 1**

In a saturated solution, an additional solute will not dissolve : kc = [Ca 2+][ CrO4 2-]

CaCrO4 is a solid, it’s omitted from the equilibrium expression. If x is concentrations of Ca2+ and CrO4 2- at the EQ : x^2 = 7.1 x 10^-4 => x = 2.7 x 10^-2

At EQ : [ Ca 2+] = [ CrO4 2- ] = 2.7 x 10^-2

**Answer 2**

[Ca2+][CrO4^2-] = 7.1 x 10^-4

Let x = molar solubility of CaCrO4

[Ca2+] = x ; [CrO4^2-] =x

x(x) = 7.1 x 10^-4

x = 2.67 x 10^-2

Answer with 2 significant figures [Ca2+] = [CrO4^2-] = 2.7 10^-2