A buffer solution is a solution that can resist pH change upon the addition of an acidic or basic component. It is able to neutralize small amounts of added acid or base, thus maintaining the pH of the solution relatively stable. This is important for processes and/or reactions that require specific and stable pH ranges. Buffer solutions have a working pH range and capacity that dictate how much acid/base can be neutralized before pH changes, and the amount by which it will change.
A buffer solution is composed of a weak acid and its conjugate base, or a weak base and its conjugate acid. To effectively maintain a pH range, a buffer must consist of a weak conjugate acid-base pair. For example, HF (hydrofluoric acid) is a weak acid, and its conjugate base is fluoride. When paired with sodium, they form a buffer solution. The bicarbonate buffering system is used to regulate the pH of blood, and bicarbonate also acts as a buffer in the ocean.
The Henderson-Hasselbalch equation expresses the pH as a function of the pKa and the ratio of the base and acid concentrations. Buffers have limits to how much they can neutralize; once this buffer reaches its capacity, the solution will act as if no buffer is present, and the pH can begin changing dramatically once again. Buffers are used in fermentation, food preservatives, drug delivery, electroplating, printing, and the activity of enzymes, as well as in the blood oxygen-carrying system.
