NH4Cl

NH4Cl, commonly known as ammonium chloride, is an inorganic compound that appears as a white crystalline solid at room temperature. It is formed by the combination of ammonia (NH3) and hydrogen chloride (HCl): NH3 + HCl → NH4Cl. Industrially it is produced as a byproduct in various chemical processes and can also be prepared by neutralizing excess HCl with ammonia. In aqueous solution, it dissociates into ammonium (NH4+) and chloride (Cl−) ions, and the solution is mildly acidic due to hydrolysis of the ammonium ion.

Physically, ammonium chloride melts at 338°C but decomposes before melting. It is highly soluble in water and also soluble in alcohols. The solid is colorless and odorless and forms a stable ionic lattice when crystallized.

NH4Cl has several common industrial and laboratory uses. It serves as a flux in soldering and brazing to remove oxides from metal surfaces. It has been used as an electrolyte in dry cell batteries and as a source of nitrogen in certain fertilizers and hydroponic systems. It is also employed as a food additive (E510) and as an acidity regulator in some products, particularly where a mild, saline flavor is desired.

In solution, ammonium chloride creates mildly acidic conditions, which can influence pH-sensitive processes. Handling requires caution: it is an irritant to skin, eyes, and the respiratory tract. Heating or strong heating may release corrosive hydrogen chloride and ammonia gases. Proper ventilation, gloves, and eye protection should be used, and it should be stored away from strong oxidizers and moisture.

See also related ammonium salts and common fluxing agents.