Question

Pure copper sulphate can be obtained from its impure sample by the process of

• A. Filtration
• B. Evaporation
• C. Crystallisation
• D. Fractional distillation

Answer 1

The correct option is C

Crystallisation

The explanation for the correct option:

Different separation techniques are present depending upon the property of the substance to be separated

(C) Crystallisation:

• The impure sample can be purified using crystallization.
• It involves the formation of solid crystals from the solution by cooling it.
• Take the sample of copper sulfate in a beaker and dissolve it in 50 mL of water by stirring it until the sample dissolves.
• Filtrate the solution and heat the set up over a sand bath which allows the water to evaporate.
• When the solution becomes concentrated, allow the sample to cool
• After some time blue-colored crystals of copper sulfate (CuSO₄) formed.
• Decant the layer of water (containing impurity). This will give the pure crystals of copper sulfate

The explanation for the incorrect option:

(A) Filtration:

• Substances that are having a size greater than 1000 nm separated from the solution or the mixture

(B) Evaporation:

• The substance which is dissolved in the solvent can be recovered by evaporating the solvent part.
• The solution of sodium chloride heated and evaporating the water content leaves sodium chloride as a white powder

(D) Fractional distillation:

• The miscible liquids have a boiling point difference of less than ${25}^{\mathrm{o}}\mathrm{c}$.
• The mixture is heated in a distillation flask where the vapors pass through the fractionating column.
• The liquid with a higher boiling point rise and falls into a distillation flask and the liquid with a lower boiling point passes through the condenser and is collected in the beaker.

Thus, option (C) i.e crystallization is used to recover a pure sample from the impure mixture