Methods of Separation - Crystallisation Method




To obtain pure copper sulphate from an impure sample.

Aim: To obtain pure copper sulphate from an impure sample

Requirements: Sample, china dish, burner, filter paper.

Principle: Heating produces a saturated solution of the salt. This solution cools and its oversaturation results in the formation of copper sulphate crystals which are free of any impurities.


  • Take some (approximately 5 g) impure sample of copper sulphate in a china dish.
  • Dissolve it in minimum amount of water.
  • Filter the impurities out.
  • Evaporate water from the copper sulphate solution so as to get a saturated solution.
  • Cover the solution with a filter paper and leave it undisturbed at room temperature to cool slowly for a day.

Observation: We could obtain crystals of copper sulphate in the china dish.

Inference/ Result: Crystallisation is a process that separates a pure solid in the form of its crystals from a solution. Hence, we could obtain pure copper sulphate.


What type of mixtures is separated by the technique of crystallization?

By the technique of crystallization, pure solids are separated from impurities. For example, salt obtained from sea is separated from impurities; crystals of alum (Phitkari) are separated from impure samples.

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