What type of chemical reaction is the reaction between an acid and a base?

The reaction between an acid and a base is called neutralization. In the simplest aqueous example, hydrogen ions from the acid react with hydroxide ions from the base to form water.

A traditional neutralization equation is acid + base → salt + water. For example, hydrochloric acid reacting with sodium hydroxide produces sodium chloride and water: HCl + NaOH → NaCl + H2O. The sodium and chloride ions are spectator ions; the essential net ionic reaction is H+ + OH− → H2O.

Neutralization is central to acid–base titrations, in which a solution of known concentration is used to determine an unknown concentration. The point at which chemically equivalent amounts have reacted is called the equivalence point. It is not always exactly pH 7: a weak acid reacting with a strong base, for example, can produce a basic solution at equivalence.

Neutralization is sometimes confused with redox, synthesis, or decomposition. Those describe different reaction patterns, although one reaction can occasionally fit more than one broad classification. The defining feature here is acid–base proton transfer.