Chemistry unit three (part two)

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  • Created on: 29-03-14 10:48
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  • Chemistry unit three (part two)
    • Types of water
      • Hard water
        • Contains dissolved compounds such as calcium and magnesium salts
        • Hard water uses more soap to produce a lather and to wash effectively because the dissolved compounds for an insoluble solid called scum. Soap less detergents do not do this.
        • When it is heated, temporary hard water produces an insoluble solid called scale. This can be deposited in kettles, boilers and popes and reduces the efficiency of them and causes blockages.
        • Calcium compounds are good for our health. They help to develop strong teeth and bones. They may also reduce the risk of heart disease.
      • Soft water
        • Lathers easily and doesn't form scum or scale
    • Removing hardness
      • Temporary hard water
        • Contains hydrogen carbonate ions, These ions decompose when heated to produce carbonate ions, water and carbon dioxide.
        • The carbonate ions react with calcium ions and magnesium ions in the water to produce precipitates of calcium carbonate and magnesium carbonated which are deposited as scale.
      • Hard water (permanent and temporary)
        • Precipitating out the ions that cause hardness softens water.
        • Adding washing soda, which is sodium carbonate, softens water. The sodium carbonate reacts with the calcium ions and magnesium ions in the water to form solid calcium carbonate and magnesium carbonate that cannot react with soap.
        • Ion exchange columns can remove hardness. They're packed with a resin containing sodium or hydrogen ions. When hard water is passed through the resin, calcium and magnesium ions attach to the resin and sodium or hydrogen ions take their place in the water.
    • Water
      • Water treatment
        • Water for drinking shouldn't contain harmful substances and should have sufficiently low levels of dissolved salt and microbes
        • Water can be trated to make it safe to drink. Water is often treated by sedimentation and filtration to remove solids. This is followed by disifection to kill microbes in the water. Chlorine is often used to kill microbes
        • Water filters can be used to improve the taste of water. They often contain carbon and an ion-exchange resin that remove soluble substances and silver or another substance to prevent the growth of disease
        • Pure water can be made by distillation. This requires a large amount of energy to boil the water so would be expensive on a large scale.
      • Water issues
        • There are advantages and disadvantages to treating water
        • Hard water causes problems but it has health benefits. If the water is not suitable for a particular purpse you can treat the water or use an alternative supply
        • Chlorine is particularly effective in killing microbes so that it is safe to use. However it is poisonous and can produce other toxic chemicals so its use must be carefully controlled
        • Fluoride compounds are added to toothpastes and to water supplies to help prevent tooth decay. Arguments against adding fluoride to water is that people should be able to choose to take extra fluoride or now.


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