Basics ‹ 57
If the compound is dissolved in H 2 O, indicated by (aq), the compound takes on the
prefix hydro and the suffix ic. If the compound is not in solution, the state of matter
should be shown as follows:
HCl(g),HF(l)If the formula has no designation of phase or water, either name may be used.
Examples for naming these compounds are:Formula Name
HCl(g) hydrogen chloride
H 2 S(g) hydrogen sulfide
HCl(aq) hydrochloric acid
H 2 S(aq) hydrosulfuric acid
HCl hydrogen chloride or hydrochloric acid
H 2 S hydrogen sulfide or hydrosulfuric acid
HCN (hydrocyanic acid) is named using these rules. However, in this case, it does
not matter if the phase or water is indicated.Ternary Compounds
Ternary compounds are those containing three or more elements. If the first element in
the formula is hydrogen, it is usually classified as an acid. If the formula contains oxygen
in addition to the hydrogen, the compound is usually classified as an oxyacid. In general, if
the first element in the formula is not hydrogen, the compound is classified as a salt.
Ternary acids are usually named with the suffixes ic or ous. The exceptions are the
acids derived from ions with an ide suffix (see HCN in the preceding section). These acids
undergo many reactions to form salts, compounds of a metal, and the ion of an acid. The
ions from the acids H 2 SO 4 and HNO 3 are SO 42 - , NO 3 -. If an acid name has the suffix ic,
the ion of this acid has a name with the suffix ate. If an acid name has the suffix ous, the
ion has a name with the suffix ite. Salts have the same suffixes as the suffixes of the ions.
The difference between the acid with a suffix ic and the acid with the suffix ous can many
times be determined by visual inspection of the formula. The acid with the suffix ous
usually has one fewer oxygen atom than the acid with the suffix ic. Examples:
Formula Name of the acid Formula Name of the acid
H 2 SO 4 sulfuric acid HNO 3 nitric acid
H 2 SO 3 sulfurous acid HNO 2 nitrous acid
When the ternary compound is not an acid, the first element is usually a metal. In these
cases, the name of the compound is simply the name of the metal followed by the name of
the ion. The ammonium ion is treated as a metal in these cases.
The following are examples:
Acid Salt
formula Acid name Ion name formula Salt name
H 2 SO 4 sulfuric acid sulfate ion Na 2 SO 4 sodium sulfate
H 2 SO 3 sulfurous acid sulfite ion Na 2 SO 3 sodium sulfite
HNO 3 nitric acid nitrate ion KNO 3 potassium nitrate
HNO 2 nitrous acid nitrite ion KNO 2 potassium nitrite
H 3 PO 4 phosphoric acid phosphate ion (NH 4 ) 3 PO 4 ammonium
phosphate