Ozone Depletion (AQA A Level Chemistry): Revision Note

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

• The ozone layer is beneficial for life on Earth because it absorbs most of the sun's harmful ultraviolet radiation

  • Ultraviolet radiation is linked to skin cancer, damaging DNA and harming marine life

• 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