Diammonium

Diammonium refers to a class of salts that contain two ammonium ions (NH4+) per formula unit, balanced by a dianionic counterion. In these salts, the general composition is (NH4)2A, where A is a dianion such as sulfate (SO4^2−), hydrogen phosphate (HPO4^2−), or carbonate (CO3^2−). The term is commonly encountered in inorganic fertilizer chemistry and in industrial salts.

Two well-known examples are diammonium sulfate and diammonium phosphate. Diammonium sulfate has the formula (NH4)2SO4 and is a white, highly soluble crystalline solid used primarily as a nitrogen fertilizer and in various industrial processes. Diammonium phosphate, often written as (NH4)2HPO4, is also a nitrogen and phosphorus source and is widely used as a fertilizer; it is sometimes referred to as diammonium hydrogen phosphate. Other diammonium salts can be formed with different dianions, such as carbonate or oxalate, yielding salts with similar stoichiometry.

Preparation typically involves neutralization of a strong acid with ammonia. For example, sulfuric acid reacts with ammonia to give diammonium sulfate: H2SO4 + 2 NH3 → (NH4)2SO4. Phosphoric acid reacts with ammonia to form diammonium phosphate: H3PO4 + 2 NH3 → (NH4)2HPO4. These salts are usually highly soluble in water and exhibit mildly acidic solutions due to the ammonium ion.

Applications and safety: The primary use of diammonium salts is as fertilizers supplying nitrogen and other nutrients. They are also used in feed additives and various industrial processes. Handling should avoid inhalation or dermal exposure, as ammonium salts can be irritating and release ammonia upon decomposition or heating.