Unit 3- Water

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  • Created by: JuanVelo
  • Created on: 24-12-15 15:22

Hard water

  • Hard water contains dissolved compounds such as calcium and magnesium salts.
  • The calcium and/or magnesium ions in hard water react with soap producing a precipitate called scum
  • One type of hard water can produce a solid scale when it is heated, reducing the efficiency of heating systems and kettles
  • Hard water is beter than soft water for developing and maintaining teeth and bones. It may also help to prevent heart disease
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Removing hardness

  • Soft water does not contain ions that produce scum or scale
  • Hard water can be softened by removing the ions that roduce scum and scale
  • Temporary hardness is removed from water by heating it. Permanent hardness is not changed by heating.
  • The hydrogencarbonate ions in temporary hard water dcompose on heating. The carbonate ions formed react with Ca2+ (aq) and Mg2+ (aq) ions, making precipitates
  • Either type of hard water can be softened by adding washing soda or by using an ion- exchange resin to remove calcium and magnesium ions
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Water treatment

  • Water for drinking should contain only low levels of dissolved substances and microbes
  • Water is made fit to drink by filtering it to remove solids and adding chlorine to reduce the number of microbes
  • We can make pure water by distillation but this requires large amounts of energy which makes it expensive 
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Water issues

  • Chlorine is added to water to sterilise it by kiling microbes
  • Fluoride helps to improve dental health
  • Some argue against the fluoridation of public water supplies. For example, they think that people should have the right to choose if they want to take extra fluoride or not
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