Nitrogen

Symbol: N
Molecular formula: N₂
Valency: 3
Position in periodic table: Group-V A, Period-2nd
Electronic configuration: 2, 5 (1S², 2S² 2P³)
Atomic number: 7
Atomic weight: 14
Molecular weight: 28 amu
Freezing point:- 210 °C
Boiling point: -196 °C

Occurrence

Nitrogen is found in both free and combined states. It occupies 78.07% by volume.

General methods of preparation of nitrogen gas

By heating copper in air:

Firstly, air is passed through lime water and then concentrated sulphuric acid to make the air free from carbon dioxide and moistures respectively. The air contains only nitrogen and oxygen which are passed over the heated copper wire as shown in the figure. Here copper combines with oxygen to make copper oxide and nitrogen gas passes over. This nitrogen can be collected by downward displacement of water.

By burning phosphorous in air:

Nitrogen gas can be prepared by burning phosphorous in air. A crucible with phosphorous is taken and allowed to float on water. Then phosphorous is burnt in crucible is covered with gas jar as shown in figure. The oxygen of the gas jar is consumed during the burning of phosphorous penta oxide is formed. The gas left in the jar is nitrogen.
4P + 5O₂ → 2P₂O₅

By decomposition of compounds containing nitrogen

Like, when dilute solution of ammonium nitrite is heated, nitrogen gas is produced.
NH₄NO₂→ N₂ +2H₂O

Laboratory preparation of nitrogen gas

Principle:
When the solution of sodium nitrite and ammonium chloride is heated they react together and liberate nitrogen gas.
NaNO₂ + NH4Cl → NaCl + H₂O +N₂

Take a mixture of ammonium Chloride and Sodium nitrate in equivalent amount in a round bottom flask. Some water is added to make the solution of the mixture. Then the delivery tube is fitted with a round bottom flask with the help of a cork. The flask is heated gently with a source of heat. After that gas is produced by the reaction of chemicals and is collected in gas jar by downward displacement of water.

Precautions

• Ammonium chloride and sodium nitrite should not be used in solid form because ammonium chloride, being a sublimate, sublimes and escape in form of vapour on heating.
• Apparatus should be made airtight.
• Ammonium chloride and sodium nitrite should be taken in equivalent amount.

Test of nitrogen

When burning magnesium ribbon is inserted in a jar containing gas, if it burns continuously and forms magnesium nitride, it proves that gas is nitrogen.

Properties of nitrogen

Physical properties

• It is neutral to the indicator.
• It is non-combustible gas but it is combustion supporter.
• It liquefies at -196°C and solidifies at -210°C.
• Nitrogen gas in generally inert, nonmetallic, colourless, odorless and tasteless.
• The atomic number of nitrogen is 7 and its atomic weight is 14.0067.
• The density of nitrogen at 0^oC is 1.251 grams/liter and its specific gravity is 0.96737.
• Nitrogen forms trivalent bonds in most compounds.

Chemical properties

• When a mixture of nitrogen and hydrogen is heated to about 500°C, at the atmospheric pressure of 200-900 atmosphere and in the presence of a catalyst finely divided iron and molybdenum, ammonia gas is liberated.
  N₂ + 3H₂ → 2NH₃
• When a mixture of nitrogen of nitrogen and oxygen is heated at 2000°C- 3000°C in electric arc, they combine together and give oxides of nitrogen.
  2N₂ + O₂ → 2N₂O (Nitrous oxide)
  N₂ + O₂ → 2NO (Nitric oxide)
  N₂ + 2 O₂ → 2NO₂ (Nitrogen dioxide)
• Reactive metals like magnesium, calcium, aluminium etc. when burnt in nitrogen forms respective nitrides.
  3Mg + N₂ → Mg₃N₂ (magnesium nitride)
  heat
  3Ca + N₂ → Ca₃N₂ (calcium nitride)
  heat
  2Al + N₂ → 2AIN (aluminium nitride)
  heat

Uses of nitrogen

• It is used to manufacture explosive.
• It is used for replacing fuel in fuel tanks in airplane.
• It is used in filling electric bulbs