Acids

An acid can be thought of as a molecule containing at least one hydrogen cation (H⁺) attached to an anion. The nomenclature of acids depends on whether the anion contains oxygen. If the anion does not contain oxygen, the acid is named with the prefix hydro- and the suffix -ic. For example, HCl dissolved in water is called hydrochloric acid. Likewise, HCN and H₂S dissolved in water are called hydrocyanic and hydrosulfuric acids, respectively.

If the anion of the acid contains oxygen, the name is formed by adding the suffix -ic or -ous to the root name of the anion. If the anion name ends in -ate, the -ate is replaced by -ic (or sometimes -ric). For example, H₂SO₄ contains the sulfate anion (SO₄²⁻) and is called sulfuric acid; H₃PO₄ contains the phosphate anion (PO₄³⁻) and is called phosphoric acid; and HC₂H₃O₂, which contains the acetate ion (C₂H₃O₂⁻), is called acetic acid. For anions with an -ite ending, the -ite is replaced by -ous in naming the acid. For example, H₂SO₃, which contains sulfite (SO₃²⁻), is called sulfurous acid; and HNO₂, which contains nitrite (NO₂⁻), is named nitrous acid. The acids of the oxy anions of chlorine are used here to illustrate the rules for naming acids with oxygen-containing cations.