Britannica Sources used in this answer

Why does an anion ending in -ate produce an acid name ending in -ic?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

The structure of phosphorous acid, H3PO3. — oxyacid The structure of phosphorous acid, H₃PO₃.

The naming convention for acids containing oxygen is determined by the suffix of the corresponding anion. When an oxyanion's name ends in -ate, the suffix is replaced by -ic (or sometimes -ric) to form the name of the acid.12

This system provides a consistent way to distinguish between related acids based on the oxygen content of their parent anions:

-ate to -ic: Anions ending in -ate (which typically contain more oxygen atoms in a series) form acids ending in -ic. For example, the sulfate anion (SO $_{4}^{2 -}$ ) forms sulfuric acid (H $_{2}$ SO $_{4}$ ).31
-ite to -ous: Anions ending in -ite (which contain fewer oxygen atoms) form acids ending in -ous. For example, the sulfite anion (SO $_{3}^{2 -}$ ) forms sulfurous acid (H $_{2}$ SO $_{3}$ ).31

This nomenclature ensures that the acid's name reflects the oxidation state or oxygen composition of the underlying polyatomic ion, allowing chemists to identify the components of the compound systematically.312