Advanced Placement (AP) Chemistry Practice Exam

What happens when a strong acid is added to a buffer system?

1. The buffer raises the pH significantly.

2. The buffer system resists a significant change in pH.

3. The buffer fully neutralizes the strong acid.

4. The buffer becomes ineffective immediately.

The correct answer is: The buffer system resists a significant change in pH.

When a strong acid is added to a buffer system, the primary function of the buffer is to resist significant changes in pH. Buffers are composed of a weak acid and its conjugate base (or a weak base and its conjugate acid), which work together to neutralize any added acids or bases. When a strong acid is introduced, the weak base component of the buffer reacts with the strong acid to form more of the weak acid component. This reaction mitigates the impact of the strong acid on the overall pH of the solution, allowing the buffer to maintain a relatively stable pH in spite of the addition of the acid. The effectiveness of the buffer depends on the concentrations of the buffer constituents and how much strong acid is added, but in general, buffers are specifically designed to manage pH changes in such scenarios. Thus, while the pH may change, it does not change significantly, illustrating the buffer's effectiveness in resisting such alterations.