Question

The method of separation of sodium chloride and ammonium chloride is:
[A] Fractional distillation
[B] Sublimation
[C] Chromatography
[D] Crystallization

Answer 1

Hint: When we heat the mixture of ammonium chloride and sodium chloride, ammonium chloride turns into vapour and sodium chloride does not. To describe this property of ammonium chloride we use a certain term and that will be the correct answer here.

Complete step by step answer:
To answer this question, let us understand what these methods mean.
Firstly, we have fractional distillation-
If we have a mixture of two or more liquids with different boiling points, we can separate them using the method of fractional distillation. It is a method used for the separation of mixture into their component parts. The liquid is heated at a temperature where one of the components of the mixture vaporizes and thus we can separate it from the rest of mixture. We use fractional distillation generally for separation of liquids having a difference of less than 25 degrees Celsius in their boiling points.

Next, we have sublimation-
It is a phase transition where the element turns into a gas phase directly from the solid phase without actually passing through the liquid state. If we have a mixture of two elements among which one sublimes and one does not, we can separate the two by the process of sublimation.
Then we have chromatography-
Paper chromatography is a method, generally used in analytical chemistry, used to separate coloured chemicals or compounds. It is a technique used for separation of different parts of a mixture of gases or liquids.

Lastly, we have crystallization-
It is a process by which we obtain a highly organised structure of the solid which is known as crystal. Crystals are formed as precipitate in the solution. Every compound gives us different types of crystals. Some are coloured while others are not. Some form needles like crystals and some are powder like. We can obtain crystals by precipitating from a solution or freezing.
In the question, we have a mixture of sodium chloride and ammonium chloride.
Ammonium chloride upon heating it turns into vapour-
     \[N{{H}_{4}}Cl(s)\to N{{H}_{3}}(g)+HCl(g)\]

Mixture of ammonium chloride and sodium chloride is white in colour but upon heating, ammonium chloride turns into vapour and sodium chloride does not thus the mixture is separated.
We can separate the above mixture through sublimation.
So, the correct answer is “Option B”.

Note: It is important to remember here that ammonium chloride does not undergo sublimation. We use the term sublimation to describe a change in physical state and not a chemical reaction like ammonium chloride upon heating turns into hydrogen chloride and ammonia. It is not sublimation but a chemical change. But since ammonium chloride turns into vapour and sodium chloride does not therefore, the method of sublimation can be used to separate the two mixtures.
Separation of a mixture of sodium chloride and camphor is an appropriate example of separation through sublimation.