Question

Absolute alcohol can be prepared from rectified spirit by _ _ _ _ _ _ distillation.
A. Vacuum
B. Fractional
C. Azeotropic
D. None of these.

Answer 1

Hint: Ethyl alcohol containing less than one percent by weight of water is called absolute alcohol and distilling ethanol-water mixtures in the presence of salt like potassium carbonate will effectively produce absolute ethanol.

Complete Step by step solution:
Absolute alcohol is considered as 100% concentrated ethanol with the molecular formula ${{C}_{2}}{{H}_{5}}OH$.
Rectified spirit is a mixture with a composition of 95 percent ethanol and 5 percent water.
To obtain a pure form of absolute alcohol, an additional one separation step is required, so that the amount of water content in the rectified spirit is removed totally.
Based on the chemical nature of ethanol and water, their concentration in the liquid mixture does not alter when heated up to its boiling point.
So we need to separate ethanol and water using azeotropic distillation. Azeotropic distillation is a method to break azeotrope where another volatile component, named the mass separating agent (MSA), is added to form a new lower-boiling azeotrope that is heterogeneous.
Ethanol-water azeotrope is usually broken with the help of toluene hence toluene acts as a mass separating agent.

According to the above information, we conclude that alcohol can be prepared from rectified spirit by azeotropic distillation. Hence the accurate answer to the given question is the option (C) azeotropic distillation.

Note: There is a possibility of confusion between extractive distillation and azeotropic distillation. We have discussed everything about azeotropic distillation where extractive distillation is a method in which specific separation solvent must be used in every mixture which should not be able to form an azeotrope.