Question

After 20.0g of `Na_2SO_4` are added to a 0.5 L saturated solution of `CaSO_4`, does the concentration of `Ca^(2+)` increase, decrease, or stay the same?

Answer 1

`[Ca^(2+)]` will reduce.

Explanation:

The calcium sulfate is saturated. That is, the reaction,

`Ca^(2+) + SO_4^(2-) rightleftharpoons CaSO_4(s)` is at equilibrium. The addition of more sulfate anion will drive the equilibrium to the right. Calcium sulfate will precipitate, with reduction in `[Ca^(2+)]`, so that the ion product resatisfies the solubility expression, `K_(sp) = [Ca^(2+)][SO_4^(2-)]`.