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Group 15: Nitrogen - Dinitrogen

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Group 15: Nitrogen - Dinitrogen - Lesson Summary

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.
 
Stage-1:
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.

                 

Stage-2:
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

      NH 4Cl (aq)         +    NaNO 2 (aq)    →         NaCl (aq)   +  NH 4NO 2 (aq)
Ammonium Chloride      Sodium Nitrite      Sodium Chloride     Ammonium Nitrite
 
        NH 4NO 2 (aq)  →           2H 2O (vap)   +    N 2 (g)
Ammonium Nitrite        Water Vapour             Dinitrogen Gas

Dinitrogen can also be obtained by thermal decomposition of ammonium dichromate.
 
(NH 4) 2Cr 2O 7                Heat →       N 2                  +      4H 2O            +     Cr 2O 3
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.
 
     2NaN 3          573 K →           2Na   ↑   +            3N 2  ↑
Sodium Azide                 Sodium            Dinitrogen Gas

   Ba(N 3) 2            573 K →              Ba             +           3N 2  ↑
Barium Azide                        Barium                Dinitrogen Gas
 
Physical properties of N2:
  • 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.

Reactivity of nitrogen:
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.

      N 2           +      3Mg                ∆ →        Mg 3N 2
Dinitogen              Magnesium              Magnesium Nitride

      N 2           +      3Ca                ∆ →        Ca 3N 2
Dinitogen              Calcium                   calcium Nitride

      3N 2           +      3Al                ∆ →        6AlN
Dinitogen              Aluminium              Aluminium Nitride
 
It also reacts with hydrogen at high temperature and pressure in the presence of a catalyst.
 
      N 2           +        3H 2                773K (High Pressure) →                          2NH 3
Dinitogen              Hydrogen                     Catalyst                                      Ammonia

Dinitrogen and oxygen react in equal volumes at a very high temperature of 2000 kelvin to form nitric oxide.
 
      N 2           +      O 2                2000K →                     2NO
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.

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