CIE AS Chemistry (9701) 2019-2021

Revision Notes

2.3.5 Uses of Halogens

Uses of Halogens

  • Halogens and their compounds have a wide range of important industrial uses but also environmental significance

Purification of water

  • Chlorine can be used to clean water and make it drinkable
  • The chlorine kills bacteria which could cause infectious diseases
  • It also prevents the growth of algae, removes bad tastes, smells and discolouration
  • However, there are some concerns associated with the use of chlorine in water purification
  • Chlorine is toxic
  • It can also react with organic substances in the water and potentially cause carcinogens


  • Chlorine is also widely used as a bleaching agent
  • It reacts with oxygen and therefore reduces dyes and pigments to become colourless
  • Household bleach is made up of dissolved calcium hypochlorite (Ca(OCl2)) and sodium hypochlorite (NaOCl) which act as disinfectant and cleaning agents
  • During the manufacturing process of bleach, harmful toxins including chlorine gas are released into the atmosphere
  • These pollutants stay in the air and cause pollution as well as damage the ozone layer


  • Chlorine is used in the manufacture of the polymer polyvinyl chloride (PVC)
  • PVC is a cheap and versatile polymer used for a wide range of purposes
    • PVC is used for windows, drainpipes, electrical cable insulation and clothing
  • However, PVC is very unreactive, so disposing of the polymer has a wide range of environmental consequences
    • PVC is non-biodegradable and takes many years to break down
    • Burning the PVC polymer release toxic fumes into the atmosphere

Use of halogenated hydrocarbons

  • The most common halogenated hydrocarbons are chlorofluorocarbons (CFCs)
  • These compounds contain carbon atoms with chlorine and fluorine atoms attached to them
    • Eg. CCl3F and CCl2F
  • CFCs have many uses due to their non-flammable and non-toxic properties
    • They are used as refrigerators
    • Propellants for aerosols
    • As solvents for dry cleaning
  • However, CFCs have adverse environmental effects
    • 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
  • Halogenated hydrocarbons are also used in making plastics such as PVC (which is a polymer made from the monomer chloroethene)

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