removing water hardness

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  • Created by: siobhan
  • Created on: 18-05-13 14:12
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  • Removing water hardness
    • Soft water may contain dissolved substances, but it does not contain dissolve salts that react with salt to form scum. Also it does not produce scale when it's heated.
    • Hard water can be made soft by removing the dissolved calcium and magnesium ions that react with soap
    • Some types of hard water are affected by heating while others are not.
      • Temporary hard water is softened by boiling because when it is heated the calcium and mangesium compounds form insoluble scale and this removes them from the water
      • Permanent hard water is not softened by boiling and does not produce scale when it is heated
    • One method of softening either type of hard water is by precipitating out the ions that cause hardness. This can be done by adding washing soda, which is sodium carbonate. The sodium carbonate reacts with the calcium and magnesium ions in the water to form solid calcium and magnesium carbonate that cannot react with soap
    • Temporary hard water contains hydrogen carbonate ions, HCO3. The hydrogen carbonate ions decompose when heated to produce carbonate ions, water and carbon dioxide: 2HCO3= CO3+ H2O+CO2
      • The carbonate ions react with calcium and magnesium ions in the water to produce precipitates of calcium carbonate and magnesium carbonate that are deposited as scale
    • Another method is to use an ion-exchange column packed with a resin containing sodium or hydrogen ions. When hard water is passed through the resin, calcium and magnesium ions become attached to the resin and sodium or hydrogen ions replace them n the water- sodium and hydrogen ions do not react with soap

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