C4 - Purifying and testing water

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  • Created by: Naomi
  • Created on: 23-01-13 21:42
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  • Purifying and testing water
    • Water purification
      • The water in a river is cloudy and often not fit to drink
        • To turn it into clean water in taps it is passed through a water purification works
      • The three stages of water purification are:
        • Sedimentation
          • Chemicals are added to make solid particles and bacteria settle out
        • Filtration
          • A layer of sand on gravel filters out the remaining fine particles
            • Some types of sand filter also remove microbes
        • Chlorination
          • Chlorine is added to kill microbes
      • Some soluble substances such as pesticides and nitrates are not removed by the standard purification method (as they are dissolved in water)
        • Extra processes are needed to remove them
      • Sea water has many sunstances dissolved in it that is undrinkable
        • Techniques such as distillation must be used to remove the dissolved substances
          • It takes huge amounts of energy, so it is very expensive and only used when there is no fresh water
    • Water tests
      • Water can be tested with precipitation reactions using aqueous silver nitrate solution and barium chloride solutions
      • In precipitation reactions, two solutions react to form a chemical that does not dissolve
        • This chemical suddenly appears in the liquid as a solid - a precipitate




Good but this is c5 not c4

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