ammoniumi

Ammonium (NH4+) is a positively charged polyatomic ion formed when ammonia (NH3) is protonated. The English term ammonium derives from ammonia, which in turn takes its name from the ancient god Ammon. In Latin texts, the form ammonii appears as the genitive of ammonium.

In aqueous solution, ammonium acts as a weak acid. The equilibrium NH4+ ⇄ NH3 + H+ has a pKa around 9.25 at 25 °C, so at neutral and acidic pH the species is predominantly NH4+, while higher pH shifts toward NH3.

Occurrence and production: Ammonium arises in nature from the decomposition of organic matter and from animal waste. Industrially, ammonia produced by the Haber-Bosch process is used to generate ammonium salts by reaction with acids. Common ammonium salts include ammonium chloride (NH4Cl), ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), and ammonium phosphate.

Biological and environmental role: In soils, ammonium is a key nitrogen source for plants. Soil microbes oxidize NH4+ to nitrite and nitrate in nitrification. In animals, ammonium is detoxified to urea in the liver. High ammonium concentrations can be toxic to some organisms and affect soil pH and nutrient balance.

Uses and safety: Ammonium salts are widely used as fertilizers and in various industrial and laboratory applications. Some salts, notably ammonium nitrate, are also restricted due to their potential explosive hazards under certain conditions. Handling requires attention to irritation, environmental release, and regulatory guidelines.