Question

How will you obtain a pure sample of copper (II) sulphate from an impure sample?

Answer 1

Pure sample of Copper (II) sulphate $\left({\mathrm{CuSO}}_4\right)$ from an impure sample can be obtained by crystallisation.

Crystallisation: Crystallisation is a technique to purify an impure sample and obtain pure solid in the form of crystals from its solution.

Process of crystallisation of pure sample of copper (II) sulphate from an impure sample:

• Prepare a saturated solution of impure copper (II) sulphate sample in a minimum amount of water.
• Then heat the solution and add more copper (II) sulphate in it.
• Filter the hot solution to separate the undissolved insoluble impurities in the solution.
• Concentrate the filtrate in the china dish and by heating it gently.
• Evaporate the filtrate till one-fourth of the solution remains in the china dish.
• Transfer the concentrated solution to the watch glass and let it cool overnight.
• Blue coloured pure crystals of Copper (II) sulphate pentahydrate are obtained.
• These crystals are washed and dried between the folds of the filter paper.