Ammonia

Ammonia is acolourless gas, NH₃, with a strong pungent odour; r.d. is 0.59 (relative to air); m.p. is -77.7°C; b.p. is -33.35°C. It is very soluble in water and soluble in alcohol. The compound may be prepared in the laboratory by reacting ammonium salts with bases such as calcium hydroxide or by the hydrolysis of a nitride. Industrially it is made by the Haber process and over 80 million tons per year are used either directly or in combination. Major uses are the manufacture of nitric acid, ammonium nitrate, ammonium phosphate and urea (the last three as fertilizers), explosives, dyestuffs and resins.

Liquid ammonia has some similarity to water as it is hydrogen bonded and has a moderate dielectric constant, which permits it to act as an ionizing solvent. It is weakly self-ionized to give ammonium ions, NH₄⁺ and amide ions, NH₂^-. It also dissolves electropositive metals to give blue solutions, which are believed to contain solvated electrons. Ammonia is an extremely soluble in water giving basic solutions that contain solvated NH₃molecules and small amounts of the ions NH₄⁺ and OH^-. The combustion of ammonia in air yields nitrogen and water. In the presence of catalysts NO, NO₂ and water are formed; this last reaction is the basis for the industrial production of nitric acid. Ammonia is a good proton acceptor (i.e. it is a base) and gives rise to a series of ammonium salts, e.g.

NH₃ + HC1 ® NH₄⁺ + Cl^-.

It is also a reducing agent.

The participation of ammonia in the nitrogen cycle is a most important natural process. Nitrogen-fixing bacteria are able to achieve similar reactions to those of the Haber process, but under normal conditions of temperature and pressure. They release ammonium ions, which are converted by nitrifying bacteria into nitrite and nitrate ions.

<== попередня сторінка	\|	наступна сторінка ==>
Journal of Electroanalytical Chemistry	\|	Texts from scientific articles

Не знайшли потрібну інформацію? Скористайтесь пошуком google:

Генерація сторінки за: 0.004 сек.