AQA Chemistry Water


Water is used as a coolant, a solvent and in many industrial applications.

Water cycle = Sun heats water -> EVAPORATION -> Water vapour cools -> CONDENSATION -> Clouds form -> TEMPERATURE DROP -> Rain falls

Hard water:

  • contains dissolved calcium and magnesium compounds
  • doesn't lather easily
  • reacts with soap to form scum (calcium stearate/magnesium stearate precipitate)
  • is created when water goes through gypsum/limestone rock
  • when heated, hard water forms limescale (calcium carbonate)

Sodium carbonate (washing soda) removes hardness by precipitating out calcium and magnesium ions.

An ion exchange column contains sodium. These ions are exchanged for magnesium and calcium ions as the water passes through the column. Softens temporarily and permanently hard water.

Boiling removes temporarily hard


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