C3.2 - Water

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  • Created by: Emily_O
  • Created on: 24-09-13 17:37

Hard and soft water

  • Soft water easily forms a lather with soap
  • Hard water contains either dissolved calcium or magnesium compounds and reacts with soap to form scum so more soap is needed to form a lather


  • Using hard water can increase costs as more soap is needed
  • Hard water is good for teeth and bones
  • May also help to lower the risk of heart disease
  • Supposedly tastes better


  • When temporary hard water is heated it can produce scale that reduces the efficiency of heating systems and kettles
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Softening hard water

There are two types of hard water:

  • Permanent hard water remains hard when boiled
  • Temporary hard water is softened by boiling and contains hydrogencarbonate ions (HCO3-) that decompose when heated to produce carbonate ions which react with calcium and magnesium ions to form precipitates

Hard water can be made soft by removing the dissolved calcium and magnesium ions which can be done by:

  • Adding sodium carbonate which reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate
  • Using commercial water softeners such as ion exchange columns whcih replace the calcium and magnesium ions when hard water passes through the column
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Purifying water

Water treatment:

  • Rainwater is collected in resevoirs
  • Aluminium sulfate and calcium oxide are added to remove dirt
  • Precipitate is allowed to settle out
  • Water is filtered through sand
  • Chlorine is added to kill bacteria
  • Water quality is tested before it's piped to consumers

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