Solubility Product

Question

A student measures the CrO₄^2- concentration in a saturated aqueous solution of silver chromate to be 1.28×10^-4 M.

Based on her data, the solubility product constant for silver chromate is...

Answer 1

Lets start with the balance equation of the dissolution of silver chromate

Ag₂CrO₄ (s)⇔ 2Ag⁺(aq) + CrO₄^2-(aq)

For every mol of Ag₂CrO₄ that is produced, we know that 2 mols of Ag⁺ ions are produced and 1 mol of CrO₄^2- ions is produced. Therefore the solubility product can be set up as follows...

K_sp = [2x]²[x] = 4x³

x represents the molar solubility of Ag₂CrO₄, which we know is 1.28E-4. So when we plug this in for x, we get.

K_sp = 4(1.28E-4)³ = 8.39E-12