Glossary
buffer
A buffer is a solution that resists a change in pH when acid or base is added, usually by pairing a weak acid with its partner base.
A buffer is a solution that holds its pH nearly steady when an acid or a base is added to it. It works by pairing a weak acid with its conjugate base: when extra hydrogen ions arrive, the base half of the pair takes them up; when they are in short supply, the acid half releases more. Both components are present before the disturbance, so the change is absorbed rather than passed on, and the pH moves a little instead of a lot. Buffers matter because biological reactions only run in a narrow window. Blood stays between pH 7.35 and 7.45 largely because of the carbonic acid and bicarbonate pair, with breathing adjusting the carbon dioxide that feeds it, and a buffer system in a laboratory keeps an enzyme working. A buffer has a limit: add enough acid and it is used up, and the pH then drops sharply.
Taught in
Related terms
- pH — pH is a measure of how acidic a solution is — how many hydrogen ions it holds — on a scale that usually runs from 0 to 14, with 7 neutral.
- acid — An acid is a substance that gives up hydrogen ions in water, which lowers pH below 7 and lets it neutralize a base.
- equilibrium — Equilibrium is the state of a reversible reaction in which the forward and reverse rates are equal, so the amounts stop changing while both directions still run.
Source: NIST periodic table and reference data for the atomic masses and half-life figures, NIH PubChem for the substance data, and NIST Special Publication 811 for the unit conventions — the same sources the chemistry guide cites. All three are US federal government material, not subject to copyright in the United States. Every definition, example and calculation above was written for this course; no dictionary or textbook text is reproduced. (NIST and PubChem accessed 2026-10-26; definitions written 2026-10-27)