Inorganic Chemistry – Nitrogen
--------------------------------------------------------------------------------------------------------------------Atomic Number: 7; Electrons Configurations: 2.5
Nitrogen has isotopes of mass number in order of adundance, 14 and 15.
Chemical Atomic Weight: 14.008
Comprises 78% of the air mixture
--------------------------------------------------------------------------------------------------------------------The Nitrogen Cycle
Nitrogen is essential to the life of both plants and animals. Plants cannot make use of natural
nitrogen in the air it is insoluble and unreactive. Plants get nitrogen by absorbing soluble nitrate
and ammonium salts in the soil. The supply must be replaced by:
1. Ammonium sulphate from the distillation of coal in the gas-works
2. Natural deposits, e.g. Chile Saltpetre, NaNO3
3. Fixation of atmspheric nitrogen in compounds by manufacture, e.g., a) Haber’s process
for ammonia, b) manufacture of calcium cyanamide
4. animal excreta
5. Thunderstorms which form nitric acid which is washed down by rain and reacts with
substances in the soil to form nitrates and ammonium compounds
6. Conversion of atmospheric nitrogen into nitrates by nitrogen-fixing bacteria in
leguminous plants. (e.g. Peas, Beans, etc)
Haber’s Process
Chemical Equation:
Raw Materials:
N 2  3H 2  2 NH 3 (H  ve)
Nitrogen (from fractional distillation of liquid air or laboratory method)
Hydrogen (from reacting natural gas with steam)
CH4 + 2H2  CO2 + 4H2
Conditions:
Conditions
Pressure
Explanation
Ammonia is formed with reduction in volume. By Le Chatelier’s principle, an
increase of pressure applied to an equilibrium mixture of nitrogen, hydrogen and
ammonia must shift the equilibrium in such a way that pressure tends to be
reduced again. Higher pressure is favourable to the production of ammonia.
Temperature Moderate Temperature around 400 to 450oC. The production of ammonia is an
exothermic reaction. By Le Chatelier’s principle, lowering of temperature of the
system in equilibrium must shift the equilibruim in such a way that the
temperature tends to be raised again. Low temperature is favourable to the
peoduction of ammonia but too low temperature will cause the reaction to be
inactive.
Catalyst
The usual catalyst on the large scale is finely divided reduced iron, promoted by
alkali or alumnia.
Properties of ammonia
Physical Properties:
 Colorless, pungent gas
 Boiling pt –33.5oC at 760 mm atm
 Alkaline gas, turns red litmus blue
 Less dense than air
 Very soluble in water
Chemical Properties:
 Dissolves in water to give alkaline solution (NH4OH)
 Only common basic gas. Neutralises acid or acid gas to form ammonium salt
 Oxidation of ammonia: 4NH3 + 3O2  6H2O + 2N2. If passed with excess of air and red
hot Pt as catalyst, Ammonia is oxidised readily to become nitric oxide and steam: 4NH3 +
5O2  4NO + 6H2O.
 Ammonia is also oxidised to nitrogen and steam by passing over CuO.
 Ammonia forms Urea with Carbon Dioxide
 Ammonia is also readily oxidised by chlorine.
 Ammonia has lone pairs in its electrons configurations.