Tutoring chemistry, you encounter acids.  The chemistry tutor shares some observations about how to name them.

New students to the acid-and-base topic hear names like hydrochloric acid, nitric acid, and sulphurous acid.  Recently I was asked why some are hydro-, while others are -ic or -ous?

Before answering the questions about naming, I should introduce the generic formula of an inorganic acid.  It goes like this:

H_nAnion,

where n, the number of H atoms, is equal to the negative charge on the anion. (An anion is a negatively charged ion.)

How to name the acid is determined by its anion, according to these three rules:

1. If the anion is a single atom, such as S or Cl, the acid is a hydro- acid, with -ic following the atom’s name.  Examples:  H₂S is hydrosulphuric acid; HCl is hydrochloric acid.
2. If the anion is an -ate, such as nitrate, the acid is -ic.  For instance, HNO₃ is nitric acid, since its anion, NO₃, is nitrate. Similarly, H₂SO₄ is sulphuric acid; you recognize its anion, SO₄, as sulphate.
3. If the anion is an -ite, such as nitrite, the acid is -ous.  Therefore, HNO₂ is nitrous acid, since its anion, NO₂, is nitrite. H₂SO₃ is sulphurous acid; note its anion, SO₃, is sulphite.

These hints should answer most questions about inorganic acid nomenclature at the high school level:)

Source: Mortimer, Charles E. Chemistry, sixth edition. Belmont, California:    Wadsworth Publishing Company, 1986.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.