Introduction to buffer solutions: overview

A buffer solution is one that resists changes in pH upon dilution or the addition of acids and bases. The pH of a buffer solution does change when diluted or when acids and bases are added but the change is much less than that compared to an unbuffered solution.

A buffer solution is usually composed of a weak conjugate acid-base pair, e.g. the ethanoic acid/ethanoate pair (acidic buffer) or the ammonium chloride/ammonia pair (basic buffer). It is most effective (or has a maximum buffer capacity) when it contains equal equilibrium concentrations of the weak acid and its conjugate base.

For an acidic buffer, we have the following equilibrium:

HA(aq)+H_2O(l)\rightleftharpoons A^-(aq)+H_3O^+(aq)

If a small amount of acid H3O+ is added to the solution, it reacts with the conjugate base A to form the weak conjugate acid HA, thereby removing the added acid and resisting the change in pH. Similarly, when a small amount of base OH is added, it combines with H3O+ to form water; again, resisting the change in pH. The degree to which a buffer solution resists the change in pH is dependent on a few factors, which shall be discussed in the next article.


Next article: Factors affecting buffer capacity
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