Advanced Placement (AP) Chemistry Practice Exam

Which change can affect the capacity of a buffer solution?

1. Adding more weak acid or base components.

2. Changing the temperature of the solution.

3. Diluting the buffer solution significantly.

4. Reducing the concentration of the conjugate acid or base.

The correct answer is: Diluting the buffer solution significantly.

A buffer solution is designed to resist changes in pH upon the addition of small amounts of strong acids or bases. The capacity of a buffer, or its ability to maintain pH, is directly related to the concentration of its weak acid and its conjugate base. When a buffer solution is diluted significantly, the concentrations of both the weak acid and its conjugate base decrease. This lowers the overall capacity of the buffer, making it less effective at neutralizing added acids or bases. Since buffering action is reliant on the presence of these components, a significant dilution means that the system has fewer moles of acid and base available to react with any added strong acid or base. Therefore, significantly diluting the buffer solution directly decreases its capacity to maintain pH stability. This highlights why this option is indeed a correct way to alter the buffer's capacity.