ammoniumiooni

The ammonium ion, NH4+, is a positively charged polyatomic ion that forms when ammonia (NH3) accepts a proton. In aqueous solution it is in equilibrium with ammonia: NH4+ ⇌ NH3 + H+. The pKa of this equilibrium is about 9.25 at 25 °C, making ammonium a weak acid that can donate a proton to bases, while ammonia acts as a weak base.

Chemically, the ammonium ion adopts a tetrahedral geometry, with four N–H bonds arranged around the nitrogen atom. It is typically found in salts, where NH4+ pairs with various anions such as chloride, sulfate, nitrate, or carbonate. Common ammonium salts include ammonium chloride (NH4Cl), ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), and ammonium carbonate ((NH4)2CO3). These salts are generally soluble in water and serve as important sources of nitrogen in agriculture and industry.

In solution, ammonium can be converted back to ammonia by reaction with bases: NH4+ + OH− → NH3 + H2O. Conversely, it can be protonated or complexed under certain conditions, and it participates in various acid–base and complexation reactions in inorganic and coordination chemistry.

Occurrence and production: industrially, ammonium ions are produced by the neutralization of ammonia with acids (for example, NH3 + HCl → NH4Cl). In the environment, ammonium is an intermediate in the biological nitrogen cycle, where it is produced by decomposition and is subsequently assimilated by organisms or oxidized to nitrite and nitrate by nitrifying bacteria.

Safety: most ammonium salts are relatively low in toxicity, but some, such as ammonium nitrate, are strong oxidizers and can pose explosion hazards under confinement or high heat. Standard chemical safety practices apply.