Preparation
Dinitrogen is produced commercially by the liquefaction and fractional distillation of air. Liquid dinitrogen (b.p. 77.2 K) distils out first leaving behind liquid oxygen (b.p. 90 K). In the laboratory, dinitrogen is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.
Small amounts of NO and HNO3 are also formed in this reaction; these impurities can be removed by passing the gas through aqueous sulphuric acid containing potassium
dichromate. It can also be obtained by the thermal decomposition of ammonium dichromate.
Very pure nitrogen can be obtained by the thermal decomposition of sodium or barium azide.
Properties
Dinitrogen is a colourless, odourless, tasteless and non-toxic gas. Nitrogen atom has two stable
isotopes: 14N and 15N. It has a very low solubility in water (23.2 cm3 per litre of water at 273 K and 1 bar pressure) and low freezing and boiling points. Dinitrogen is rather inert at room temperature because of the high bond enthalpy of NºN bond. Reactivity, however, increases rapidly with rise in temperature. At higher temperatures, it directly combines with some metals to form predominantly ionic nitrides and with non-metals, covalent nitrides. A few typical reactions are:
It combines with hydrogen at about 773 K in the presence of a catalyst (Haber’s Process) to form ammonia:
Dinitrogen combines with dioxygen only at very high temperature (at about 2000 K) to form nitric oxide, NO.
Uses: The main use of dinitrogen is in the manufacture of ammonia and other industrial chemicals containing nitrogen, (e.g., calcium cyanamide). It also finds use where an inert atmosphere is required (e.g., in iron and steel industry, inert diluent for reactive chemicals). Liquid dinitrogen is used as a refrigerant to preserve biological materials, food items and in cryosurgery.
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