What happens to the pH of a buffer solution when a small amount of strong acid is added?

When a small amount of strong acid is added to a buffer solution, the primary function of the buffer is to resist significant changes in pH. A buffer typically consists of a weak acid and its conjugate base, which work to neutralize added acids and bases.

In this scenario, when strong acid is introduced, it increases the concentration of hydrogen ions (H⁺) in the solution. However, the buffer components will react to this addition. The weak base present in the buffer will neutralize some of the excess hydrogen ions by converting into its conjugate acid form.

Although the reaction absorbs some of the added protons, resulting in a slight increase in the concentration of the conjugate acid, the overall change in pH is minimized. Therefore, while the pH of the buffer will decrease slightly due to the introduction of the strong acid, the buffer's capacity ensures that this change is not drastic. The equilibrium set by the buffer system allows for a moderated response to the addition of strong acids, which leads to the correct observation that the pH decreases only slightly rather than dramatically changing or becoming neutral.