Dinitrogen is abundantly available in the earth’s atmosphere and accounts for 78 % by volume of it. Dinitrogen is mainly obtained by the fractional distillation of liquid air. It is also the commercial method to prepare dinitrogen. The process of obtaining dinitrogen from air involves 2 stages.
Air is subjected to liquefaction. During liquefaction, a high pressure of 100 to 200 atmospheres is applied over dry air followed by expansion through a fine jet .This process is repeated several times to obtain liquid air.
The liquid air is subjected to fractional distillation. As dinitrogen has a lower boiling point - 77.2 kelvin than liquid oxygen - 90 kelvin - it distils off first, leaving behind liquid oxygen. Thus, in this stage, dinitrogen is isolated from liquid air.
In the laboratory, dinitrogen is generally prepared by gently heating equimolar aqueous solutions of ammonium chloride and sodium nitrite
Cl (aq) + NaNO2
(aq) → NaCl (aq) + NH4
Ammonium Chloride Sodium Nitrite Sodium Chloride Ammonium Nitrite
(aq) → 2H2
O (vap) + N2
Ammonium Nitrite Water Vapour Dinitrogen Gas
Dinitrogen can also be obtained by thermal decomposition of ammonium dichromate.
O + Cr2
Ammonium Dichromate Dinitrogen Gas Water Vapour Chromium Oxide
Sodium azide or barium azide, when heated carefully to about 573 kelvin, undergoes thermal decomposition to produce dinitrogen.
2Na ↑ + 3N2
Sodium Azide Sodium Dinitrogen Gas
Ba + 3N2
Barium Azide Barium Dinitrogen Gas
Physical properties of N2:
Reactivity of nitrogen:
- Dinitrogen is a colourless, odourless and tasteless non-toxic gas.
- Its vapour density is 14. Hence, it is slightly lighter than air.
- It can be condensed to a colourless liquid that boils at 77.2 kelvin and can be solidified under high pressure to a white snow-like mass that melts at 63 kelvin.
- It is diamagnetic in nature.
- It is slightly soluble in water. The solubility of dinitrogen at 273 kelvin and one bar pressure is found to be 23.2 ml per one litre of water.
A molecule of dinitrogen consists of a triple bond that has very high bond dissociation energy of 945.4 kilojoules per mole. Hence, dinitrogen is inert at room temperature. At high temperatures, dinitrogen reacts directly with metals such as magnesium, calcium and aluminium to form the respective nitrides.
Dinitogen Magnesium Magnesium Nitride
Dinitogen Calcium calcium Nitride
Dinitogen Aluminium Aluminium Nitride
It also reacts with hydrogen at high temperature and pressure in the presence of a catalyst.
Dinitogen Hydrogen Catalyst Ammonia
Dinitrogen and oxygen react in equal volumes at a very high temperature of 2000 kelvin to form nitric oxide.
Dinitogen Oxygen Nitric Oxide
Uses of dinitrogen:
Being inert in nature, it has many uses in industry and other walks of life.
- It is widely used as an inert atmosphere in iron, steel and other metallurgical industries.
- It dilutes the activity of oxygen in natural processes such as combustion and respiration.
- It is used in the preservation of packaged food material.
- A large amount of dinitrogen is used in the preparation of ammonia by Haber’s process.
- Dinitrogen is also used in the preparation of nitrolim which is an important fertiliser.
- Liquid dinitrogen is used as a refrigerant to preserve biological material. It is also used in cryosurgery to remove warts and other skin lesions.