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  • Water
    • Drinking water
      • water naturally contains microorganisms & dissolved salts
      • 1 passed through a filter bed to remove solid particles
      • 2 chlorine gas is added to kill any harmful microorganisms
      • 3 fluoride is added to drinking water in order to reduce tooth decay (too much can cause discolouration)
      • Can be passed through a filter containing carbon, silver & ion exchange resins
      • Any water can be distilled to produce pure water (no dissolved substances)
        • water boiled then condensed (expensive & a lot of energy)
    • Hard and soft water
      • Soft water  = not many dissolved compounds (forms a lather readily with soap)
      • Hard water contains magnesium & calcium dissolved from rocks naturally
        • hard water reacts with soap to scum, an oily substance, making it harder to form a lather
          • soapless detergents don't form scum
      • temp hard water contains hydrogencarbonate ions (HCO3^-)
        • they decompose upon heating to produce carbonate ions (CO3^2-)
          • These carbonate ions react with calcium and/or magnesium ions to form precipitates
      • advantages of hard water: good for health (bones & teeth & reduces risk of heart disease)
        • Disadvantages of hard water: more soap is needed to form a lather (cost) & leads to deposits (scale) which reduces efficiency of systems & appliances
    • Removing hardness
      • dissolved magnesium & calcium ions are removed by :
        • adding sodium carbonate solution (washing soda) to react to produce calcium carbonate & magnesium carbonate (insoluble precipitates out of solution)
        • pass water through an ion exchange column ( resin that supplies hydrogen ions or sodium ions) As hard water passes through the resin, the calcium & magnesium ions are replaced by sodium & hydrogen ions


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