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Chapter 3: Acid–Base Titration Back To Chapter

3.12: Buffers: Overview

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Analytical Chemistry

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Buffers: Overview

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3.13: Buffers: Buffer Capacity

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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.

3.12: Buffers: Overview

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.

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