Buffers

Adding a small amount of acid or base to a solution can cause a significant decrease or increase in the pH. However, many chemical and biochemical processes need a stable pH to function. Buffers can prevent a drastic change in the pH of a solution when their buffering capacity is not exceeded.

Buffers contain a weak acid and its conjugate base or a weak base and its conjugate acid. For example, human blood maintains its pH near 7.4 with a buffer composed of carbonic acid, a weak acid, and bicarbonate ions, its conjugate base.

Conjugate acid-base pairs form buffers as they do not neutralize their conjugate acid or base. For example, acetic acid and acetate cannot react. However, if acetic acid, a weak acid, and ammonia, a weak base, are added together, they will react to form a salt—ammonium acetate.

In a buffer, the weak acid neutralizes any added base by reacting with the hydroxide ions produced, whereas its conjugate base neutralizes any added acid by reacting with any hydronium ions. A similar mechanism works in the case of a weak base and its conjugate acid.

Two beakers, X and Y, contain the same volume of different solutions, each with a pH of 7.2. The solution in beaker X is