Chemistry C3.2

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  • Chemistry C3.2
    • Hard water
      • Hard water contains dissolved compounds such as calcium and magnesium salts
      • The calcium & magnesium ions in hard water react with soap producing a precipitate called scum
      • Temporary hard water can produce a solid scale when it is heated, reducing the efficiency of heating systems & kettles
      • Hard water is better than soft water for developing and maintaining teeth & bones. It may also prevent heart disease
    • Removing hardness
      • Soft water does not contain salts that produce scum or scale
      • Hard water can be softened by removing the salts that produce 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 decompose on heating
        • The carbonate ions formed react with Ca²+ and MG²+, making precipitates
      • Both types of hard water can be softened by adding washing soda or by using an ion-exchange resin to remove calcium & magnesium ions
    • Water treatment
      • Water for drinking should contain only low levels of dissolved substances & microbes
      • Water is made fit to drink by filtering it to remove solids and adding chlorine to kill microbes
      • We can make pure water by distillation but this requires large amounts of energy which makes it expensive
    • Water issues
      • There are advantages & disadvantages to any type of water treatment
      • Water can be treated to remove hardness, to remove harmful microbes and to improve dental health


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