Dinitrogen makes up to 78% of the earth’s atmosphere and it is the most abundant element present in the air and the seventh most abundant uncombined element found in the universe. This element was first discovered in the year 1772 by a Scottish physician Daniel Rutherford. The symbol of this chemical element is N and 7 is its atomic number.
Preparation of dinitrogen:
Nitrogen is obtained commercially by liquefaction and fractional distillation of air. This process mainly involves two steps:
Step 1: Air is reduced to liquid air by applying high pressure ranging between 100 and 200 atmospheres. This compressed air is then passed through fine jet where it undergoes expansion. This method is repeated several times which results in the formation of liquid air.
Step 2: The liquid formed undergoes fractional distillation. The boiling point of dinitrogen is lower than that of the liquid oxygen and hence it distils out, leaving behind liquid oxygen. Nitrogen is obtained from the impure liquid.
In laboratory, dinitrogen is obtained by reacting aqueous solution of ammonium chloride with sodium nitrite.
NH4Cl(aq) + NaNO2(aq) → N2(g)+ 2H2O(l) + NaCl(aq)
The products obtained consists of impurities such as NO and HNO3 which can be removed by thermal decomposition of ammonium dichromate. Another method to remove the impurities is to pass the gaseous mixture through sulphuric acid containing potassium dichromate.
(NH4)2Cr2O7 → N2+ 4H2O+ Cr2O3
Decomposition of sodium or barium azide in the presence of high temperature also results in the formation of pure nitrogen.
Physical properties of Dinitrogen:
- Nitrogen is a colourless, odourless and diamagnetic in nature. It is a non-toxic gas.
- It is sparingly soluble in water.
- Nitrogen undergoes condensation to form a colourless liquid which on solidification results in the formation of snow like mass.
Chemical properties of Dinitrogen:
- Dinitrogen has a high bond enthalpy due to the N = N bond. Due to this it is inert at room temperature. However the reactivity increases as the temperature increases. At high temperatures, nitrogen molecules react with metals to form respective ionic nitrides and with non-metals to form covalent nitrides.
- At about 773 K it reacts with hydrogen to form ammonia in Haber’s Process.
- Nitric oxide is formed when nitrogen molecule reacts with oxygen molecule at a temperature of 2000 K.
Uses of Dinitrogen:
- It is mainly used in the industrial manufacturing of compounds such as ammonia, calcium cyanamide etc.
- It is used in the manufacturing industries such as iron and steel to obtain an inert atmosphere.
- Liquid nitrogen is used in food industries as a preservative and as a refrigerant.
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