12.4    Uses of Halogens

• Chlorine is used in the chlorination of water to kill bacteria. The chlorine undergoes disproportionation

Cl2(aq) + H2O(l) → HCl(aq) + HClO(aq)

Chloric(I) acid, HClO produced decomposes slowly to produce reactive oxygen atoms that kill bacteria in water.

HClO → HCl + O

• Bleach is an equal mixture of sodium chloride, NaCl and sodium chlorate(I), Sodium chlorate(I) is a powerful oxidising agent and bleaches dye and other coloured molecules by oxidising them.
  • Halogens are also used in chlorofluorocarbons(CFCs). CFCs are widely used as refrigerants, propellants and They are also used as solvents for dry cleaning and generating foamed plastics like expanded polystyrene or polyurethane foam.
  • Unfortunately, CFCs are largely responsible for destroying the ozone layer. In the high atmosphere, the carbon-chlorine bonds break to give chlorine free radicals and these radicals destroy the ozone. CFCs are now being replaced by less environmentally harmful compounds.
  • Plastic PVC(poly(chloroethene) or polyvinyl chloride) are made from halogen compounds
  • Poly(chloroethene) is made through polymerisation of organic molecules, the organic molecule is chloroethene, CH2 These organic molecules join together repeatedly to form the polymer.

• • Poly(chloroethene) is used to make a wide range of things including guttering, plastic windows, electrical cable insulation, sheet materials for flooring and other uses, footwear, clothing, and so on
• Bromine and iodine are often used in the manufacture of dyes and drugs