Question

What process will you use to separate common salt from a common salt solution?
A. Sublimation
B. Centrifugation
C. Evaporation
D. Distillation

Answer 1

Hint: Sodium chloride is simply the chemical name of common salt.
Salts are generally solids and so they have very high melting and boiling points.
The boiling point of water is less than that of common salt and so water can be removed at first by heating.

Complete step by step answer:
The process of sublimation is the transition of a substance from solid phase directly into the gas phase without undergoing the liquid phase in between. The solid substance which undergoes the process of sublimation is said to be ‘sublime’ or a sublimating substance.
This sublimation process is used to separate and purify those substances from a mixture which can sublimate on heating. For example, iodine and ammonium chloride are two sublimating substances.
Common salt is not a sublimating substance and so it cannot be separated from its solution by sublimation. So, A is wrong.
Centrifugation is a separation technique which is most commonly used to separate particles from a solution on the basis of their shape, size, viscosity, density and rotor speed. So, it cannot be used to separate common salt from its solution and so B is also wrong.
Common salt mixes up with water very easily to form a clear solution. Water has a much lower boiling point than the salt and so when a common salt solution is heated, water will evaporate at first. Common salt will not evaporate and hence, its crystals will be left behind. Thus, the evaporation technique can be used to separate common salt from its solution and so A is correct.
Distillation is used to separate components of a mixture based on the difference in their boiling points. In simple distillation, a mixture is heated so that the most volatile component is converted from liquid to vapour.

Thus, D is incorrect.

Note:
Common salt is most commonly used in the preparation of food and also as a preservative in pickles.
Another important use of common salt is in the melting of ice and also as a raw material for the making of a large number of useful chemicals in industry like sodium carbonate, sodium hydroxide, baking soda etc.