Description
Molecular mass of ammonia: 17.03 g/mol
Reaction: pH 9-11 depending on concentration
Ammonia water (NH4OH) is a solution of ammonia (NH₃) in water, characterized by a specific, pungent odor. It is a substance with an alkaline pH due to the partial dissociation of the ammonia contained in it, leading to the formation of ammonium and hydroxide ions. In addition, it contains ammonia molecules with a tetrahedral structure, consisting of 3 nitrogen bonds with hydrogen molecules and a non-bonding lone electron pair on the nitrogen atom. The shape of the ammonia molecule resembles a trigonal pyramid, while the presence of lone-pair electrons causes a slight distortion of the tetrahedral structure. Care should be taken when handling ammonia water, as it can cause irritation. In addition, it can react with oxygen, chlorine and iodine. When ammonia water is heated or treated with strong bases, it can release ammonia gas. It is classified as a dangerous material with the number UN 2672 according to the ADR regulations.
Knowledge of ammonia water and ammonia dates back to ancient Egypt and Arabia. Interestingly, ammonia compounds can also be found in space; the first ammonia molecule outside Earth was discovered in 1968, and the presence of this compound is known even on the gaseous planets of the Solar System.
On an industrial scale, ammonia water is obtained by the absorption of ammonia gas in water. Ammonia gas is usually produced through the Haber-Bosch process, which involves the reaction of nitrogen and hydrogen at high pressure in the presence of an iron catalyst, often enriched with aluminum oxides (Al₂O₃) or potassium oxides (K₂O) to increase its activity and stability. This is an exothermic and reversible reaction. The obtained gaseous ammonia is introduced into water in special absorption columns. The process takes place in a closed system, where water flows in the opposite direction to the ammonia gas (countercurrent flow), increasing the efficiency of absorption. The solubility of ammonia in water can be increased by lowering the temperature or increasing higher reaction pressure. Ammonia water can also be obtained in the laboratory, where solid ammonia (in the form of ammonium bicarbonate, NH₄HCO₃) is dissolved in water. The substance dissociates, releasing ammonia into the solution. Moreover, the hydrolysis of ammonium salts is also used, leading to the release of ammonia, which is followingly dispersed in water. Ammonia water can also be obtained through the reaction of an ammonium salt with a strong base. Historically, distillation of organic materials, such as coal, peat or plant waste, was also used. The gaseous ammonia obtained in this way dissolves in water and forms ammonia water. In the past, coke was used in this process.
Ammonia water reacts with acids and acid oxides to form ammonium salts. It also reacts with hydrogen sulphide (H2S), where ammonium sulphide is formed. The ammonia contained in ammonia water is a ligand, so it forms complexes with transition metals. In addition, ammonia can both reduce halogens, such as chlorine, and be oxidized by strong oxidants. Ammonia water can react with some salts, causing their decomposition, and also react with some aldehydes and ketones, leading to the formation of imines or amines.
