Gas Percentage in Air Percentage in Inhaled Air Percentage in Exhaled Air
Nitrogen 79 79 79
Oxygen 20 20 17
Argon 0.9 1 (with other Inert Gases) 1 (with other Inert Gases)
Carbon Dioxide 0.03 Trace 4
Others 0.07
Water Variable Saturated


Fractional Distillation of Air – the main industrial method of preparation of pure oxygen and nitrogen

  • Air is liquefied by compression and cooling to below the boiling point of both oxygen and nitrogen, so that most of the “air” becomes a
  • The liquid “air” is allowed to warm slowly and the nitrogen (b.p. -195°C) boils off first and thus can be
  • The oxygen (b.p. -183°C) boils off after the nitrogen and can then also be


Pollutants Cause Effect Solution
Sulphur Dioxide Combustion of Sulphur (found in fossil fuels) Forms acid rain when reacted with water in clouds Scrubbing – converts SO2  to H2SO4

S(s) + O2(g) -> SO2(g)

SO2(g) + H2O(l) -> H2SO3(aq)

Nitrogen Oxides Reaction between nitrogen and oxygen at high temp and pressure in motor vehicle engines Contributes to Acid Rain and are a major component of photochemical smog Catalytic Converters

2N2(g) + 3O2(g) -> 2NO(g) + 2NO2(g)

Carbon Monoxide Incomplete combustion in motor vehicle engines Strong bonds with haemoglobin, decreasing the amount of oxygen distributed around the body Catalytic Converters
Lead Combustion of petrol containing lead Brain damage, nervous system problems Catalytic Converters, using unleaded fuel


Catalytic Converter –catalysts that convert poisonous exhaust fumes into harmless gasses in cars.


  • The reduction catalyst uses platinum and rhodium to help reduce the NOx emissions by ripping the nitrogen atom out of the molecule, freeing the

2NO -> N2 + O2 / 2NO2 -> N2 +  2O2

  • The oxidation catalyst removes the unburned hydrocarbons and carbon monoxide by burning them over a platinum and palladium

2CO + O2  -> 2CO2

  • 2NO2 + 4CO -> 4CO2 + N2