Preparation and Properties of Nitrogen:
In the free state, nitrogen constitutes three-fourths of air by weight or four-fifths by volume of air. In a combined state, it is found as saltpetre (KNO3), chile saltpetre (NaNO3) etc.
Preparation of Nitrogen:
Nitrogen is prepared from two main sources, namely air and nitrogenous compounds.
(1) From Air- Nitrogen can be obtained from air by the following methods-
(a) By passing air free from carbon dioxide and water vapour over red hot copper.
|2Cu + O2 (from air) ————> 2CuO + N2|
(b) By burning phosphorous in a vessel of air over water. Phosphorous pentoxide formed in the process dissolves in water forming phosphoric acid and nitrogen is left behind.
|P4 + 5O2 (from air) ————> P4O10 + N2|
P4O10 + 6H2O ————> 4H3PO4
(c) By fractional distillation of liquid air.
(2) From Nitrogenous Compounds- Nitrogen may be obtained from nitrogenous compounds as under-
(a) By heating ammonium dichromate, (NH4)2Cr2O7.
|(NH4)2Cr2O7 —–Heat——> N2 + Cr2O3 + 4H2O|
(b) By the action of ammonia on chlorine, calcium hypochlorite, bleaching powder etc.
|8NH3 + 3Cl2 ————> N2 + 6NH4Cl|
4NH3 + 3Ca(OCl)2 ————> 2N2 + 3CaCl2 + 6H2O
2NH3 + 3CaOCl2 ————> N2 + 3CaCl2 + 3H2O
(c) By the action of sodium hypobromite on urea.
|3NaOBr + NH2CONH2 ————> 3NaBr + CO2 + 2H2O + N2|
Laboratory preparation of Nitrogen- Nitrogen is prepared in the laboratory by heating a saturated solution containing equimolecular quantities of ammonium chloride (NH4Cl) and sodium nitrite.
|NH4Cl + NaNO2 ————> NaCl + NH4NO2|
NH4NO2 ————> N2 ↑+ 2H2O
Method- Take a concentrated solution containing ammonium chloride and sodium nitrite in a round-bottomed flask. Fit up the flask with a thistle funnel and a delivery tube that dips underwater in a trough. Heat the flask gently. Collect the nitrogen so obtained by the downward displacement of water.
Drying of Nitrogen gas- Nitrogen gas so obtained is contaminated with moisture. It is dried by passing the gas through Anhydrous calcium chloride or phosphorous pentoxide and then collecting the same over mercury.
Properties of Nitrogen gas:
Physical Properties of Nitrogen gas:
- It is a colourless, odourless and tasteless gas.
- It is very slightly soluble in water.
- It is slightly lighter than air.
- It is not poisonous in nature but animals die in an atmosphere of nitrogen gas for want of oxygen.
- It liquefies to a colourless liquid (boiling point -196°C) and freezes to give a white solid (melting point -210°C).
Chemical Properties of Nitrogen gas:
Chemically, nitrogen is comparatively an inert or inactive gas.
(1) Nature- Nitrogen is neither acidic nor basic but it is neutral to litmus.
(2) Combustion- Nitrogen is neither combustible nor a supporter of combustion. When a burning splinter is introduced into a jar of nitrogen gas, it neither burns nor supports combustion.
(3) Action of Non-metals-
(a) Action of Oxygen- Nitrogen combines with oxygen under an influence of an electric arc (3000-3500°C) giving rise to the formation of nitric oxide (NO).
|N2 + O2 ————> 2NO|
(b) Action of Hydrogen- It reacts with hydrogen in the presence of finely divided iron (Fe) and molybdenum (Mo) at 450°C and under a pressure of 200 atmospheres giving rise to the formation of ammonia.
|N2 + 3H2 ⇌ 2NH3|
(c) Action of Halogens- Nitrogen does not react with halogens directly but halogens react with ammonia to give rise to the formation of nitrogen halides like nitrogen trichloride NCl3 etc.
|NH3 + 3Cl2 ————> NCl3 (Explosive liquid) + 3HCl|
NH3 + 3I2 ————> NI3 (Explosive solid) + 3HI
(4) Action of Metals- Nitrogen combines with various metals such as Na, Mg and Al to give rise to the formation of the corresponding nitrides.
|6Na + N2 ————> 2Na3N|
3Mg + N2 ————> Mg3N2
2Al + N2 ————> 2AlN
(5) Action of Calcium Carbide- On heating calcium carbide (CaC2) in an atmosphere of nitrogen at 1000°C, calcium cyanamide is formed which is a valuable fertilizer.
|CaC2 + N2 ————> CaCN2 + C|
Uses of Nitrogen:
- In filling electric bulbs and high temperature thermometers.
- As a food by the plants.
- In providing an inert atmosphere in certain metallurgical processes.
- In diluting oxygen of air so as to make combustion much less rapid.
- In refrigeration purposes in the form of liquid nitrogen.
- In the manufacture of a number of important compounds like ammonia, nitric acid, calcium cyanamide.