Acid Nomenclature

Remember that the names of Arrhenius acids usually end in acid (hydrochloric acid, sulfuric acid, nitric acid ) and that their formulas fit one of two general patterns:

HX(aq)       X = F, Cl, Br, or I

H_aX_bO_c

For example, HCl(aq) (hydrochloric acid), H₂SO_4, (sulfuric acid), and HNO₃ (nitric acid) represent acids.

Names and Formulas for Binary Acids

Binary acids are named by writing hydro followed by the root of the name of the halogen, then -ic, and finally acid:

hydro(root)ic acid

The only exception to remember is that the “o” in hydro is left off for HI(aq), so its name is hydriodic acid (an acid used to make pharmaceuticals).

Most chemists refer to pure HCl gas as hydrogen chloride, but when HCl gas is dissolved in water, HCl(aq), the solution is called hydrochloric acid. We will follow the same rule in this text, calling HCl or HCl(g) hydrogen chloride and calling HCl(aq) hydrochloric acid. The same pattern holds for the other binary acids as well.

You will be expected to be able to write formulas and names for the binary acids found below . Remember that it is a good habit to write (aq) after the formula.

HF(aq) - hydrofluoric acid

HCl(aq) - hydrochloric acid

HBr(aq) - hydrobromic acid

HI(aq) - hydriodic acid

H₂S(aq) - hydrosulfuric acid

HF - hydrogen fluoride or hydrogen monofluoride

HCl - hydrogen chloride or hydrogen monochloride

HBr - hydrogen bromide or hydrogen monobromide

HI - hydrogen iodide or hydrogen moniodide

H₂S - hydrogen sulfide or dihydrogen monosulfide

Names and Formulas for Oxyacids

To name oxyacids, you must first be able to recognize them by the general formula H_aX_bO_c, with X representing an element other than hydrogen or oxygen. It will also be useful for you to know the names of the polyatomic oxyanions, because many oxyacid names are derived from them. If enough H⁺ ions are added to a (root)ate polyatomic ion to completely neutralize its charge, the (root)ic acid is formed ( See below. ).

• If one H⁺ ion is added to nitrate, NO₃^-, nitric acid, HNO₃, is formed.
• If two H⁺ ions are added to sulfate, SO₄^2-, sulfuric acid, H₂SO₄, is formed.
• If three H⁺ ions are added to phosphate, PO₄^3-, phosphoric acid, H₃PO₄, is formed.

Notice that the whole name for sulfur, not just the root, sulf‑, is found in the name sulfuric acid. Similarly, although the usual root for phosphorus is phosph-, the root phosphor‑ is used for phosphorus-containing oxyacids, as in the name phosphoric acid.

NO₃^- is nitrate, and HNO₃ is nitric acid.

C2H₃O₂^- is acetate, and HC₂H₃O₂ is acetic acid.

SO₄^2- is sulfate, and H₂SO₄ is sulfuric acid.

CO₃^2- is carbonate, and H₂CO₃ is carbonic acid.

PO₄^3- is phosphate, and H₃PO₄ is phosphoric acid.