Question

Common salt is obtained from sea water by :

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

Answer 1

The correct option is A

Evaporation

Correct Answer: Option(A) Evaporation

The explanation for the correct answer:

1. Evaporation: The process of obtaining a non-volatile soluble solid from its solution by allowing the liquid component to vaporize is called evaporation.
2. Seawater, when enclosed in shallow pits, evaporates naturally under the sunlight into vapour, leaving behind a residue containing salt.
3. The residue was then purified by crystallization in order to obtain pure common salt.
4. Crystallization: The process of cooling a hot, concentrated solution of a substance to obtain crystals of pure solid is called crystallisation.

The explanation for the incorrect answer:

1. Option (B) Sublimation: The process of conversion of a solid substance directly into its vapours on heating and vapour into solid on cooling is called sublimation. There is no sublimable substance in sea water thus this technique can not be used.
2. Option (C) Filtration: The process of separating suspended solid matter from a liquid, by causing the latter to pass through the pores of a filter is called filtration. Sea water contains salt dissolved in water. It form a homogeneous mixture and salt cannot be filtered thus this technique can not be used.
3. Option (D) Fractional distillation: The process of separation of two or more miscible liquids with the difference in their boiling points close to each other into individual components by distillation is called fractional distillation.

Common salt is obtained from seawater by (Option(A)) Evaporation