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What is Crystallization?

It is a process that separates pure solid from an impure solution in the form of c rystals.


In this case, 

  1. A solution is heated in an open container. 
  2. Then it is left to cool .

After some time, pure solids are formed in the form of crystals.


Application or Uses of Crystallization

  • Separation of Salt from Sea Water
  • Separation of Crystals of Alum from impure samples
  • Separation of Pure Copper Sulphate from impure Sample


  1. Take some amount of impure copper sulphate solution in a china dish
  2. Dissolve it in minimum amount of water
  3. Filter the impurities
  4. Heat and evaporate the water to get a saturated solution
  5. Cover the solution with filter paper and leave it undisturbed for 1 day to cool down at room temperature
  6. Crystals are formed, while impurities are left in the solution
  7. Pour the cooled solution through a filter paper, to obtain the crystals and dry.

We will obtain pure crystals of Copper Sulphate on the filter paper



Why is Crystallization a better technique than Evaporation?

  • During evaporation, we heat the solid. While heating, some solids get decomposed or charred (burnt)
    Example - Sugar.
    This is not a problem in Crystallisation

  • In evaporation, some impurities remain dissolved even after filtration.  These may contaminate solid during the process of evaporation.
    These impurities get removed in cyrstallisation


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CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Accounts and English at Teachoo