When comparing Q and Ksp for an unsaturated solution, which statement is correct?

• A. Q < Ksp
• B. Q = Ksp
• C. Q > Ksp
• D. Q = Ksp = 0

Answer: (C)

The key idea is to compare the actual ion product in solution to the solubility product constant. Q uses the current concentrations of the dissolved ions, while Ksp is the value at equilibrium for dissolution at a given temperature.

For an unsaturated solution, the ion concentrations are still below what they would be at equilibrium, so the product of those concentrations is less than Ksp. That means there is capacity to dissolve more solid until the system reaches equilibrium and Q climbs to match Ksp. If Q were to equal Ksp, the solution would be at equilibrium (saturated). If Q exceeded Ksp, the solution would be supersaturated and precipitation would occur to bring Q back down toward Ksp.

So, in an unsaturated solution, Q is less than Ksp.