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Buffer

A buffer is a solution of a weak acid and its conjugate base (or a weak base and its conjugate acid), which resists large changes in pH when a little acid or base is added. Blood, for example, is buffered around pH 7.4, which is essential for cells to function.

buffer=weak acid+conjugate base\text{buffer} = \text{weak acid} + \text{conjugate base}the composition of a buffer

Example

A mixture of acetic acid and sodium acetate keeps pH nearly unchanged even if a small amount of strong acid or base is added.

Buffer capacity is greatest when the amounts of acid and conjugate base are roughly equal.
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← Strong and weak acids · Le Chatelier's principle →

Part of General Chemistry: Acids, bases and equilibrium.