CIE IGCSE Chemistry

Revision Notes

11.1.1 Water

Water: Chemical Tests, Treatment & Uses

Chemical tests for water

  • Cobalt (II) chloride turns blue to pink on the addition of water. This test is usually done using cobalt chloride paper
  • The equation is:
CoCl2(s) + 6H2O(l) → CoCl2.6H2O(s)
  • Anhydrous copper (II) sulfate turns white to blue on the addition of water
  • The equation is:
CuSO4(s) + 5H2O(l) → CuSO4.5H2O(s)

Water treatment

  • Untreated water contains soluble and insoluble impurities
  • Insoluble impurities include soil, pieces of plants and other organic matter
  • Soluble impurities include dissolved calcium, metallic compounds and inorganic pollutants
  • Filtration is the process used to remove large insoluble particles by passing the water through layers of sand and gravel filters that trap larger particles
  • But bacteria and other microorganisms are too small to be trapped by the filters so chlorination is used
  • This involves the careful addition of chlorine to the water supply which kills bacteria and other unwanted microorganisms
  • Cholera and typhoid are examples of bacterial diseases which can arise by the consumption of untreated water


Water treatment, IGCSE & GCSE Biology revision notesDiagram showing the stages in the treatment of water


Uses of water

Water in industry

  • As a coolant to reduce the temperature of some industrial processes e.g: in nuclear power plants
  • Watering crops
  • As a solvent in many chemical production processes
  • Hydroelectric power stations to generate electricity
  • As a first raw material for many processes e.g: the production of ethanol from ethene and steam (water)

Water in homes

  • Drinking, cooking and washing
  • General sanitation.
  • In car radiators, for gardens and plants

Exam Tip

Exam questions on water treatment always focus on either filtration or chlorination. You should be able to explain how each process works and the reason for each one.

Extended Only

An Inadequate Supply of Water

  • Clean and safe water supply is very important to mankind
  • Many problems arise in the event of an inadequate water supply, including:
    • Food shortages and famine due to a lack of crops which cannot grow without a clean water supply
    • Poor sanitation leads to the spread of bacteria and disease as drinking water becomes infected

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