AQA AS Chemistry

Revision Notes

3.3.4 Ozone Depletion

Uses

Fluorohalogenoalkanes

  • The most common halogenoalkanes are chlorofluorocarbons (CFCs)
  • These compounds contain carbon atoms with chlorine and fluorine atoms attached to them
    • E.g. CCl3F and CCl2F2
  • CFCs have many uses due to their chemical inertness as they are non-flammable and non-toxic
    • They are used as refrigerators
    • Propellants for aerosols
    • As solvents for dry cleaning

Hydrofluorocarbons

  • Hydrofluorocarbons (HFCs) are compounds that contain a carbon attached to hydrogen and fluorine atoms only
    • Eg. CH2F-CF3
  • As with CFCs, HFCs are chemically inert and are therefore used for a wide range of purposes

Halogenoalkanes & The Ozone Layer

  • Though chlorofluorocarbons (CFCs) have many beneficial uses, they also have devastating effects on the ozone layer:
    • CFCs absorb a lot of UV radiation in the upper atmosphere
    • The CFCs are then broken down by the UV light causing the formation of chlorine radicals
    • These radicals react with ozone and break down the ozone layer
  • This is why hydrofluorocarbons (HFCs) are often used as an alternative to CFCs
  • As these compounds don’t contain any chlorine atoms, they will not have adverse effects on the ozone layer

Chlorine radicals and the ozone layer 

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