Neutralisation is the reaction of an acid with a base that results in the pH moving towards seven. It is a useful process that occurs in everyday life such as in the treatment of acid indigestion and the treating of acidic soil by adding lime.

When an acid is neutralised, its pH increases towards seven. When an alkali is neutralised, its pH decreases towards seven.

Several different bases can neutralise acids, and water is always produced as a result of these reactions.

Equations for neutralisation

\[Acid + alkali \to salt + water\]

\[Acid + metal\,oxide \to salt + water\]

Metal oxides and alkalis are two types of base. Basic substances neutralise acids, resulting in the pH of the acid increasing towards 7, and water being produced. A soluble base dissolves in water to form an alkali.

Naming salts

To name the salt, the metal ion from the alkali (or base) replaces the hydrogen ion from the acid - (alkali to front, acid to back). For example:

\[\begin{array}{l} \text{Hydrochloric acid} + \text{sodium hydroxide} \to \\ \text{sodium chloride} + \text{water} \end{array}\]

Acid nameSalt name ending
Hydrochloric acid...chloride
Sulfuric acid...sulfate
Nitric acid...nitrate

During every neutralisation reaction, water is formed.