When an acid and an alkali (also known as a base) are mixed together, a chemical reaction called neutralisation occurs. During neutralisation, the hydrogen ions (H+) from the acid combine with the hydroxide ions (OH-) from the alkali to form water (H2O). The other ions present in the acid and alkali react to form a salt.

The overall reaction for neutralisation can be represented as follows:

Acid + Alkali → Salt + Water

For example, when hydrochloric acid (HCl) and sodium hydroxide (NaOH) are mixed, the following reaction occurs:

HCl + NaOH → NaCl + H2O

In this reaction, the hydrogen ions from HCl combine with the hydroxide ions from NaOH to form water, while the sodium ions (Na+) from NaOH combine with the chloride ions (Cl-) from HCl to form sodium chloride (NaCl).

The products of neutralisation are typically a salt and water. The salt is a compound that contains the positively charged ions from the alkali and the negatively charged ions from the acid. The water is a neutral compound that is formed by the combination of hydrogen ions and hydroxide ions.

Neutralisation reactions are important in many chemical processes, including the production of salts, the manufacture of soaps and detergents, and the control of acidity and alkalinity in various industries.