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  • water
    • potable water; is water thats been treated
      • its not pure
      • pH between 6.5 and 8.5, low salt level, no bacteria
    • 1. filtration- a wire mesh screens out large twigs
      • 2. gravel and sand beds filter out any smaller particles
        • 3. sterilisation- the water is sterilised to kill and harmful bacteria. this is done by bubbling chlorine gas through it or by using ozone or ultraviolet light
    • if a substance is soluble it will dissolve in a certain amount of solvent
      • 1. Measure accurately 100 cm3 of water and add to a beaker
        • 2.Add small amounts of the solute until no more can dissolve
          • 3. Record the mass of an evaporating dish
            • 4. Filter the mixture so the undissolved solid is left behind and the solution is in the evaporating dish
              • 5. Remove the water by heating or evaporation
                • 6. Weigh the evaporating dish with the solute in it and calculate the mass of the solute that was dissolved
      • solids become more soluble as temperature increases
    • soft and hard water
      • hard water contains Mg and Ca ions
        • happens when the water comes into contact with rocks (permanent contains   (CaSO4))
        • temporary hardness    (caused by    Ca(HCO3)2) is removed by boiling water, which leaves a layer of limescale
        • improves health care
        • some people prefer the taste
        • helps reduce heart disease
        • limescale
        • pipes can 'fur up' causing blockages
      • hard water can be softened using..
        • ion exchange
        • sodium carbonate
      • soft water lathers easily with soap hard water doesn't
    • salt water can be desalinated
  • 1. put a known volume of water into a boiling tube
    • 2. add soap solution one drop at a time and shake
      • 3. record the number of drops needed to make i lather
    • soft water lathers easily with soap hard water doesn't


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