A saturated solution of copper(I) sulfide, Cu₂S, contains 1.91 × 10^–12 g of Cu₂S dissolved in 1 dm³ of water. (A_r values: Cu = 63.5, S = 32.1)

a. Write an equilibrium expression for the solubility product of copper(I) sulfide.

b. Calculate the value of the solubility product of copper(I) sulfide, stating the units.

c. Copper(II) chromate has a solubility of 1.9 × 10^–3 mol dm^–3 in water. Copper(II) sulfate has a solubility of 1.4 × 10^–1 mol dm^–3 in water. What will you observe when 10 cm³ of an aqueous solution of 0.0100 mol dm^–3 copper(II) sulfate is added to an equal volume of a saturated solution of copper(II) chromate. Explain your answer.