🧠 The prediction rule: compare Q with K_sp

When two ionic solutions are mixed, the ions become diluted in the new total volume. Use these diluted concentrations to calculate the ion product, Q. Q has the same mathematical form as K_sp, but it uses the concentrations at that moment rather than at equilibrium.

Three-case rule

Q < K_sp: no precipitate forms. Q = K_sp: the solution is just saturated. Q > K_sp: the mixture is supersaturated and a precipitate forms until equilibrium is restored.

Words that earn marks

Use the phrase “Because Q is greater than K_sp, the solution is supersaturated and a precipitate forms.” This is stronger than writing “it goes cloudy” with no reason.