Acids usually have two names, the chemical and the common. The chemical names are given according to certain rules based upon the elements in the acid. The common name of the acid is the commercial name.
When there are three or four acids formed of the same elements, oxygen is one of the elements and is the only element varying in amount, as in: HNO3, HNO2, HNO; and HClO, HClO2, HClO3, HClO4.
The one with the most oxygen is called perchloric acid HClO4, "per" meaning "above." The most common of the above acids is HClO3, chloric acid. HClO2 is called chlorous acid, and HClO hypochlorous acid, "hypo" meaning "under" or "lesser." When there are two salts composed of the same elements, the one with the smaller proportion of the non-metallic element usually ends in ous. The one with the larger proportion ends in ic. To illustrate: CuCl2 is cupric chloride, and CuCl is cuprous chloride. FeCl2 is ferrous chloride, and FeCl3 is ferric chloride. The ending of a binary salt is always ide.
Salts with more than two elements or radicals are called tertiary compounds. When there are more than two salts, the ending ic acid is changed to ate, for example, per-ic acid is changed to per-ate; the ending ous acid is changed to ite, for example, hypo-ous acid to hypo-itc.