Monammonium

Monammonium is not a single distinct chemical species in standard nomenclature. Rather, the term is sometimes used to indicate a salt or compound that contains a single ammonium (NH4+) cation per formula unit. In practice, most references treat ammonium as the cation and use the specific salt name to identify the accompanying anion. The best-known example of a monoammonium salt is monoammonium phosphate, also called ammonium dihydrogen phosphate, with the formula NH4H2PO4.

Monoammonium salts are formed by protonating a base with one equivalent of an acid, yielding compounds in which one ammonium cation balances the charge of the anion. Monoammonium phosphate (MAP) is widely used as a fertilizer because it supplies both nitrogen and phosphorus. MAP is highly soluble in water and is produced by reacting phosphoric acid with ammonia or by neutralizing ammonia with phosphoric acid in appropriate proportions. MAP often appears in formulations for crop nutrition and can also function as a buffering and fluxing agent in some industrial processes.

Other monoammonium salts exist for different acids, though the exact stability and practical use depend on the particular anion. In many contexts, the term monoammonium appears primarily in the name of a specific compound (for example, monoammonium phosphate) rather than as a standalone chemical identity.

Nomenclature can be a source of confusion because “ammonium” designates the NH4+ cation in salts, while the broader concept of monoammonium relates to salts containing a single ammonium unit. Related compounds include diammonium salts, such as diammonium phosphate, which contain two ammonium cations per anion.