Acids are defined as substances that have a sour taste, a low pH (<7), and cause litmus paper to turn red. They also react with bases (yielding water and ionic compounds called salts) and produce hydrogen gas when used to dissolve metals such as zinc and iron.
Chemically, an acid is a molecule or ion that acts as a proton or hydrogen ion donor (Brønsted-Lowry acid) in a non-aqueous solution. In water, acids form hydronium ions (H3O+).
An acid is alternatively defined as a molecule or ion that accepts an electron pair (Lewis acid). One example is trifluoroborane, which has a boron atom capable of accepting an electron pair from ammonia (NH3) to form NH3-BF3.
Common inorganic acids include hydrochloric, sulfuric, nitric, and phosphoric acids. Common organic acids include acetic, benzoic, citric, and lactic acids.
In the laboratory, acids are used as reagents or catalysts in many types of chemical reactions.
Strong acids, such as sulfuric and hydrochloric acid, are highly corrosive and have extensive commercial applications.
- Sulfuric acid is used to process petroleum and minerals and to make other chemicals like nitric acid
- Hydrochloric acid is used to pickle steel and other metals
- Some acids are used as neutralizers to produce salts; for example, ammonium nitrate is produced by the reaction of nitric acid with ammonia
- Many acids are also used in the food and beverage industry
Acids are available in concentrated form or in solutions and in a variety of grades based on purity, including reagent (ACS), laboratory, and other technical and specialty preparations.