If Q < Ksp, what happens to the solution?

If Q < Ksp, what happens to the solution?

• A. A precipitate forms immediately.
• B. The solution is at equilibrium.
• C. More solid can dissolve.
• D. The solution becomes supersaturated.

Answer: (C)

When Q is less than Ksp, the solution is undersaturated with respect to the dissolved ions. The solid can keep dissolving to raise the ion concentrations until the ion product reaches Ksp, so more solid can dissolve. A precipitate would form only if Q were greater than Ksp, and equilibrium occurs when Q equals Ksp. Supersaturation implies Q exceeds Ksp, which isn’t the case here.

When Q is less than Ksp, the solution is undersaturated with respect to the dissolved ions. The solid can keep dissolving to raise the ion concentrations until the ion product reaches Ksp, so more solid can dissolve. A precipitate would form only if Q were greater than Ksp, and equilibrium occurs when Q equals Ksp. Supersaturation implies Q exceeds Ksp, which isn’t the case here.