If Q is larger than Ksp, what is expected to occur?

If Q is larger than Ksp, what is expected to occur?

• A. precipitation will occur
• B. dissolution will accelerate
• C. equilibrium is reached
• D. no change

Answer: (A)

The main idea is how the reaction quotient compares to the solubility product for a sparingly soluble salt. If Q is larger than Ksp, the ion concentrations in solution are higher than what can be sustained at equilibrium, so the solution is supersaturated. The system responds by forming solid until the ion concentrations drop enough that Q falls to equal Ksp. That means precipitation will occur to reestablish equilibrium. Dissolution would raise ion levels further, not help, and no change would ignore the driving force to remove excess ions.

The main idea is how the reaction quotient compares to the solubility product for a sparingly soluble salt. If Q is larger than Ksp, the ion concentrations in solution are higher than what can be sustained at equilibrium, so the solution is supersaturated. The system responds by forming solid until the ion concentrations drop enough that Q falls to equal Ksp. That means precipitation will occur to reestablish equilibrium. Dissolution would raise ion levels further, not help, and no change would ignore the driving force to remove excess ions.