Hydrochloric acid has the chemical formula HCl. It is an aqueous solution of hydrogen chloride, which when in a saturated form contains about 43% hydrogen chloride. Hydrogen chloride in aqueous solution is a strong electrolyte because it disassociates to form ions, H⁺ and Cl^-. This disassociation is complete so no molecules of HCl are found. Hydrochloric acid is a proton donor, this is the hydrogen ion. When ionization occurs only one hydrogen ion is produced per molecule of HCl, which is an example of a monoprotic acid. Because ionization is so complete with hydrochloric acid it is regarded as a strong acid and the maximum number of hydrogen ions are freed up per molecule. Hydrochloric acid is used in a wide range of chemical reactions and conversions.

Hydrochloric acid can be used to clean metal surfaces and can be found naturally occurring in the stomachs of...