What is a buffer solution?

A buffer solution is defined as a solution that resists changes in pH when small amounts of acid or base are added. This characteristic arises from the presence of a weak acid and its conjugate base, or a weak base and its conjugate acid, in equilibrium within the solution. When an acid is added, the conjugate base reacts with the excess hydrogen ions (H⁺), effectively minimizing the increase in acidity. Conversely, when a base is added, the weak acid can donate protons to counteract any increase in pH. This ability to maintain pH stability is essential in many biological and chemical systems where pH can affect reactions and processes.

In this context, it is crucial to understand why the other options do not accurately describe a buffer solution. For instance, a solution that drastically increases in pH when acid is added fails to exhibit the buffering characteristic, as it would not resist changes in pH. A solution that has a fixed pH regardless of the amount of solute does not allow for any fluctuation in pH, which is contrary to how buffers function. Lastly, a solution consisting solely of strong acids or bases does not qualify as a buffer, since strong acids and bases fully dissociate in solution and do