Ammonia - hydrogen nitride - one of the most important compounds of nitrogen and hydrogen. It is a gas without color, but with a pungent smell. The chemical composition reflects the formula of ammonia - NH3. Increasing pressure or lowering the temperaturesubstance leads to its transformation into a colorless liquid. Gaseous ammonia and its solutions are widely used in industry and agriculture. In medicine, 10% ammonium hydroxide is used - ammonia.
The structure of the molecule. Electronic formula of ammonia
The molecule of hydrogen nitride in shape resemblesa pyramid, in the base of which there is nitrogen, connected with three atoms of hydrogen. N-H bonds are strongly polarized. Nitrogen attracts the binding electron pair more strongly. Therefore, the negative charge accumulates on the N atoms, the positive charge is concentrated on hydrogen. The model of the molecule, the electronic and structural formula of ammonia, gives an idea of this process.
Hydrogen nitride dissolves very well in water(700: 1 at 20 ° C). The presence of practically free protons leads to the formation of numerous hydrogen "bridges" that connect the molecules together. Features of the structure and chemical bonding also lead to the fact that ammonia is easily liquefied by increasing pressure or by lowering the temperature (-33 ° C).
origin of name
The term "ammonia" was introduced into scientific use in1801 at the suggestion of the Russian chemist Ya. Zakharov, but the substance of mankind is familiar from ancient times. A gas with a pungent odor is released when decaying the products of vital activity, many organic compounds, for example, proteins and urea, during the decomposition of ammonium salts. Historians of chemistry believe that the substance was named after the ancient Egyptian god Amun. In North Africa there is an oasis of Siwa (Ammon). Surrounded by the Libyan desert, there are ruins of an ancient city and a temple, next to which there are deposits of ammonium chloride. This substance in Europe was called "Ammon's salt." There is a tradition that the inhabitants of the oasis Siwa sniffed salt in the temple.
Preparation of hydrogen nitride
English physicist and chemist R. Boyle in experiments burned manure and observed the formation of white smoke over a stick moistened with hydrochloric acid and introduced into the jet of the resulting gas. In 1774 another British chemist, D. Priestley, heated ammonium chloride with hydrated lime and separated the gaseous substance. Priestley called the compound "alkaline air," because his solution showed the properties of a weak base. The Boyle experiment, in which ammonia was reacted with hydrochloric acid, was explained. Solid ammonium chloride of white color occurs when the molecules of reacting substances come into contact directly in the air.
The chemical formula of ammonia was established in1875 by the Frenchman K. Bertolle, who conducted an experiment on the decomposition of matter into composite components under the action of an electric discharge. Until now, the experiments of Priestley, Boyle and Berthollet have been reproduced in laboratories for the production of hydrogen nitride and ammonium chloride. The industrial method was developed in 1901 by A. Le Chatelier, who received a patent for the method of synthesis of matter from nitrogen and hydrogen.
Ammonia solution. Formula and properties
An aqueous solution of ammonia is usually recorded as hydroxide-NH4OH. It exhibits the properties of a weak alkali:
- dissociates into NH ions3 + H2O = NH4OH = NH4+ + OH-;
- color the phenolphthalein solution in crimson color;
- interacts with acids to form salt and water;
- precipitates Cu (OH)2 as a bright blue substance when mixed with soluble copper salts.
Equilibrium in the reaction of ammonia withthe water is displaced towards the raw materials. Preheated hydrogen nitride burns well in oxygen. Oxidation of nitrogen occurs to diatomic molecules of simple matter N2. The reducing properties of ammonia are also manifested in the reaction with copper (II) oxide.
The value of ammonia and its solutions
Hydrogen nitride is used in the production of saltsammonium and nitric acid - one of the most important products of the chemical industry. Ammonia serves as a raw material for the production of soda (according to the nitrate method). The content of hydrogen nitride in an industrial concentrated solution reaches 25%. In agriculture, an aqueous solution of ammonia is used. Formula of liquid fertilizer - NH4OH. The substance is directly used as a top dressing. Other ways of soil enrichment with nitrogen are the use of ammonium salts: nitrates, chlorides, phosphates. In industrial conditions and agricultural premises it is not recommended to store together mineral fertilizers containing ammonium salts with alkalis. If the integrity of the package is violated, the substances can react with each other to form ammonia and release it into the air of the premises. The toxic compound adversely affects the respiratory system, the central nervous system of man. A mixture of ammonia and air is explosive.</ p>