Binary Acids
Some compounds containing hydrogen are members of an important class of substances known as acids. The chemistry of these compounds is explored in more detail in later chapters of this text, but for now, it will suffice to note that many acids release hydrogen ions, H+, when dissolved in water. To denote this distinct chemical property, a mixture of water with an acid is given a name derived from the compound’s name. If the compound is a binary acid (comprised of hydrogen and one other nonmetallic element):
- The word “hydrogen” is changed to the prefix hydro-
- The other nonmetallic element name is modified by adding the suffix –ic
- The word “acid” is added as a second word
For example, when the gas HCl (hydrogen chloride) is dissolved in water, the solution is called hydrochloric acid. Several other examples of this nomenclature are shown in the table below:
| Name of Gas | Name of Acid |
|---|---|
| HF(g), hydrogen fluoride | HF(aq), hydrofluoric acid |
| HCl(g), hydrogen chloride | HCl(aq), hydrochloric acid |
| HBr(g), hydrogen bromide | HBr(aq), hydrobromic acid |
| HI(g), hydrogen iodide | HI(aq), hydroiodic acid |
| H2S(g), hydrogen sulfide | H2S(aq), hydrosulfuric acid |
Oxyacids
Many compounds containing three or more elements (such as organic compounds or coordination compounds) are subject to specialized nomenclature rules that you will learn later. However, we will briefly discuss the important compounds known as oxyacids, compounds that contain hydrogen, oxygen, and at least one other element, and are bonded in such a way as to impart acidic properties to the compound (you will learn the details of this in a later chapter). Typical oxyacids consist of hydrogen combined with a polyatomic, oxygen-containing ion. To name oxyacids:
- Omit “hydrogen”
- Start with the root name of the anion
- Replace –ate with –ic, or –ite with –ous
- Add “acid”
For example, consider H2CO3 (which you might be tempted to call “hydrogen carbonate”). To name this correctly, “hydrogen” is omitted; the –ate of carbonate is replace with –ic; and acid is added—so its name is carbonic acid. Other examples are given in the table below. There are some exceptions to the general naming method (e.g., H2SO4 is called sulfuric acid, not sulfic acid, and H2SO3 is sulfurous, not sulfous, acid).
| Formula | Anion Name | Acid Name |
|---|---|---|
| HC2H3O2 | acetate | acetic acid |
| HNO3 | nitrate | nitric acid |
| HNO2 | nitrite | nitrous acid |
| HClO4 | perchlorate | perchloric acid |
| H2CO3 | carbonate | carbonic acid |
| H2SO4 | sulfate | sulfuric acid |
| H2SO3 | sulfite | sulfurous acid |
| H3PO4 | phosphate | phosphoric acid |