Question

Crystals of pure copper sulphate are separated from the solution by:
a.) Condensation
b.) Distillation
c.) Solidification
d.) Filtration

Answer 1

Hint: Copper sulphate,$CuS{{O}_{4}}$, is known as blue vitriol, due to its blue colour. It is an inorganic compound and can be gained by an electrolysis process. Pure samples can be obtained from an impure sample by recrystallization.

Complete Solution :
- Crude copper sulphate is a mixture of copper sulphate with various impurities that certainly include copper carbonate, copper oxides, and other copper compounds.
- Copper sulphate is an inorganic compound, which can be obtained by electrolysis.
- Electrolysis is a process where sulphuric acid is used in solution and copper is used as electrodes.
- It is important for us to know that impure copper is used as anode and pure copper as cathode.
- Crystallization is a process where a chemical is converted to a solid crystalline state from a liquid state.
- Crystallization of copper sulphate is done by dissolving it in water and adding a small quantity of dilute sulphuric acid to prevent the process of hydrolysis.
- The impurities left behind in the solution are removed by the process of filtration. The filtrate obtained, is concentrated to the crystallization point and then cooled.
- On cooling, transparent blue crystals of copper sulphate separate. The copper sulphate crystal formed has a triclinic shape, transparent, and is blue in colour.
So, the correct answer is “Option C”.

Note: The filtrate obtained should be evaporated only up to the crystallisation point and never be heated to dryness. Heating of the solution is often avoided. If the crystals obtained are very small, the solution has been concentrated more than required at the crystallization stage.