Question

Which of the following is used to obtain pure copper sulphate in the form of crystals from its saturated solution?

• A. Evaporation
• B. Fractional distillation
• C. Distillation
• D. Crystallization

Answer 1

The correct option is D

Crystallization

The explanation for the correct option -

• Crystallization is a process that separates a pure solid in the form of its crystals from its saturated solution.
• Take the saturated Copper sulphate$\left({\mathrm{CuSO}}_4\right)$ solution, and heat it continuously till most of the water gets evaporated.
• Now, cool down the solution so as to obtain the pure crystals of the solid.
• After that the Copper sulphate crystals are separated by filtration and dried.

The explanation for the incorrect options -

• Option A is incorrect because evaporation is a process of conversion of liquid into its vapours, even before reaching its boiling point. Copper sulphate also evaporated with water in the case of the evaporation process. After filtration, impurities remain dissolved in the solution and can contaminate the solid copper sulphate.
• Option B is incorrect because fractional distillation is the process of separating two (or more) miscible liquids by distillation, the distillate is collected in fractions boiling at different temperatures. This method is used to separate a liquid from another liquid depending on the difference in their boiling points.
• Option C is incorrect because distillation is the process of separation of a liquid from its solution with a solid constituent by heating the liquid to its vapor form and then cooling the vapor to get back the pure liquid.

Hence, Option D is the correct answer.