Hard Water

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  • Created by: Sophie
  • Created on: 02-05-13 19:35
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  • Hardness of Water
    • Hard water makes scum and scale
      • Soft water= Lather  Hard water=scum
        • Unless using a soapless detergent
        • Dissolved Ca ions and Mg ions make scum which is insoluble
          • Wastes soap
    • Mg and Ca ions
      • Water seeps through rocks, dissolving compounds like magnesium sulfate and calcium sulfate
      • Ca Helps teeth and bones
      • Reduces risk of heart disease
    • Remove the dissolved Ca2+ and Mg2+ ions to make water soft
      • Temporary hardness is caused by the hydrogencarbonate ion HCO3-
        • Removed by boiling; when heated hydrogencarbonate decomposes to produce calcium carbonate which is insoluble (limescale)
      • Permanent hardness is caused by dissolved calcium sulfate
      • Add washing soda (sodium carbonate). The carbonate ions react with the Mg and Ca ios and make an insoluble precipitate of calcium carbonate and magnesium carbonate. Ions no longer in water so its not hard.
      • Ion exchange column
        • Contains a column of beads made from resin. Salt is added and the Na+ ions stick to beads. When hard water flows through, the Na+ ions unstick and Ca and Mg ions stick to beads
          • Ca2+ and Mg2+ removed from water, replaced by Na+
    • Titration to compare hardness of water samples
      • Burette full of 50cm3 of soap solution. 50cm3 of first water in a flask. Use burette to add 1cm3 of soap solution to flask. Bung on flask and shake for 10s. Repeat these steps until a good lasting lather is formed (bubbles for at least 30s) Record how much soap was needed. Repeat with other water samples. Boil fresh samples and repeat.
      • Distilled water contains no hardness so minimum soap was needed
      • Temporary hardness seen as water is boiled
    • Drinking Water needs to be good quality
      • No poisions or microbes
      • Reservoirs
      • Water runs through mesh screen to remove big bits like twigs
        • Chemicals added to make solids and microbes stick together and fall to the bottom
          • Water filtered through gravel beds to remove all solids
            • Water is chlorinated to kill off any harmful microbes left
      • Some people buy filters containing carbon or silver
        • Carbon removes chlorine taste, silver kills bugs
        • Hard water softeners contain ion exchange resins
      • Pure water from distillation
    • Flouride and Chlorine
      • Flouride reduces tooth decay
        • In high doses is can cause cancer and bone problems
          • Worries about 'mass medicating'
      • Chlorine prevents disease
        • Chlorine linked to an nincrease in cancers. Can react with other natural substances to produce toxic-by-products
      • Monitored


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