Question

Purity of water can be checked by:
(A) Distillation
(B) Crystallization
(C) Centrifugation
(D) None of the above

Answer 1

Hint: Most of the organic and inorganic reactions are carried out in presence of water. The purity of water is determined by various methods. The impure water contains the dissolved salt. This dissolved salt alters the melting and boiling point of the substance. The water vapour condenses at the ${100}^{0}C$ and if impurities are present, the boiling point increases and the melting point decreases.

Complete step by step solution:
Distillation is widely used for the separation of components of the mixture. It is based on the principle of varying boiling points. Each component of a mixture has a certain boiling point.
The boiling point is the temperature of the liquid at which the vapour pressure of the liquid becomes equals to the atmospheric pressure.
The distillation technique is widely used for the purification of water. It produces distilled or extra pure water. Every substance has a unique boiling point at which it escapes from the liquid state to the gaseous state. On condensation, we can get the purest form of the substance.
Water can be purified through the distillation. The pure water (water-free from any impurities) boils at the${100}^{0}C$.
Impure water contains the dissolved salt which alters the temperature of the boiling point. The salts can increase or decrease the boiling point of water. The greater is the amount of dissolved salt in the water, the more will be the boiling point of the water.
The crystallisation process is also a technique to purify the solid. The common procedure involves the heating and gradually cooling of the solution. On cooling, the solid reappears as the pure crystal. The crystallisation process applies to the crystallization of solid. The purity of the water cannot be determined by the crystallization process.
The process of the centrifugation process is used for the separation of fluids, gaseous, or liquid-based on their densities. It is a separation technique, but cannot be utilised to purify the water.
Therefore, the purity of water is checked by the process of distillation.

Hence, (A) is the correct option.

Note: There are various techniques to check the purity of the water. One of the methods is evaporation. If any salt is dissolved in the water then on evaporation of water the salt remains as the residue. If the water is pure, then the pure water on evaporation leaves no residue.