Buffers play a crucial role in stabilizing the pH of a solution by mitigating the effects of small amounts of added acid or base. They consist of a weak acid and its conjugate base or a weak base and its conjugate acid. A solution of acetic acid and sodium acetate is an example of a buffer that consists of a weak acid and its salt: CH₃COOH (aq) + CH₃COONa (aq). An example of a buffer that consists of a weak base and its salt is a solution of ammonia and ammonium chloride: NH₃ (aq) + NH₄Cl (aq).

This combination prevents significant pH changes as long as the buffer's capacity is not exceeded. For example, human blood uses a carbonic acid-bicarbonate buffer system to maintain its pH near 7.4. In a buffer, the weak acid component neutralizes added bases by reacting with hydroxide ions, while the conjugate base neutralizes added acids by reacting with hydronium ions.