When Q equals Ksp, the solution is at which state?

When Q equals Ksp, the solution is at which state?

• A. Equilibrium
• B. Supersaturated
• C. Undersaturated
• D. Precipitation

Answer: (A)

This question tests how the reaction quotient Q relates to the solubility product Ksp to determine the system’s state. Q is the product of the ion concentrations, [A+][B−], at any moment, while Ksp is the maximum product that can exist when the solid is in equilibrium with the ions. When Q equals Ksp, dissolution and precipitation occur at equal rates, so there is no net change and the system sits in balance with the solid present. The solution is saturated with respect to that salt. If Q were smaller, it would be undersaturated and more solid would dissolve; if Q were larger, it would be supersaturated and precipitation would occur to restore equality. Therefore, the state is equilibrium.

This question tests how the reaction quotient Q relates to the solubility product Ksp to determine the system’s state. Q is the product of the ion concentrations, [A+][B−], at any moment, while Ksp is the maximum product that can exist when the solid is in equilibrium with the ions. When Q equals Ksp, dissolution and precipitation occur at equal rates, so there is no net change and the system sits in balance with the solid present. The solution is saturated with respect to that salt. If Q were smaller, it would be undersaturated and more solid would dissolve; if Q were larger, it would be supersaturated and precipitation would occur to restore equality. Therefore, the state is equilibrium.