Naming Acids and Bases

 

Learning Objective

  • Convert between the structure of an acid or base and its chemical name

Key Points

    • Acids are named based on their anion — the ion attached to the hydrogen. In simple binary acids, one ion is attached to hydrogen. Names for such acids consist of the prefix “hydro-“, the first syllable of the anion, and the suffix “-ic”.
    • Complex acid compounds have oxygen in them. For an acid with a polyatomic ion, the suffix “-ate” from the ion is replaced with “-ic.”
    • Polyatomic ions with one extra oxygen (as compared to the typical polyatomic ion) have the prefix “per-” and the suffix “-ic.”
    • Polyatomic ions with one fewer oxygen have the suffix “-ous”; ions with two fewer have the prefix “hypo-” and the suffix “-ous.”
    • Strong bases with “-OH” (hydroxide) groups are named like ionic compounds. Weak bases are named like molecular compounds or organic compounds.

Term

  • polyatomic ionA charged species (ion) composed of two or more atoms covalently bonded. Also known as a molecular ion.

Naming Acids

Acids are named by the anion they form when dissolved in water. Depending on what anion the hydrogen is attached to, acids will have different names.

Simple acids, known as binary acids, have only one anion and one hydrogen. These anions usually have the ending “-ide.” As acids, these compounds are named starting with the prefix “hydro-,” then adding the first syllable of the anion, then the suffix “-ic.” For example, HCl, which is hydrogen and chlorine, is called hydrochloric acid.

Nomenclature of common acidsThis chart provides the nomenclature of some common anions and acids

More complex acids have oxygen in the compound. There is a simple set of rules for these acids.

  1. Any polyatomic ion with the suffix “-ate” uses the suffix “-ic” as an acid. So, HNO3 will be nitric acid.
  2. When you have a polyatomic ion with one more oxygen than the “-ate” ion, then your acid will have the prefix “per-” and the suffix “-ic.” For example, the chlorate ion is ClO3. Therefore, HClO4 is called perchloric acid.
  3. With one fewer oxygen than the “-ate” ion, the acid will have the suffix “-ous.” For example, chlorous acid is HClO2.
  4. With two fewer oxygen than the “-ate” ion, the prefix will be “hypo-” and the suffix will be “-ous.” For example, instead of bromic acid, HBrO3, we have hypobromous acid, HBrO.

Naming Bases

Most strong bases contain hydroxide, a polyatomic ion. Therefore, strong bases are named following the rules for naming ionic compounds. For example, NaOH is sodium hydroxide, KOH is potassium hydroxide, and Ca(OH)2 is calcium hydroxide. Weak bases made of ionic compounds are also named using the ionic naming system. For example, NH4OH is ammonium hydroxide.

Weak bases are also sometimes molecular compounds or organic compounds because they have covalent bonds. Therefore, they are named following the rules for molecular or organic compounds. For example, methyl amine (CH3NH2) is a weak base. Some weak bases have “common” names. For example, NH3 is called ammonia; its name isn’t derived from any naming system.