Question

Absolute alcohol can be prepared from rectified spirit by:

• A. Azeotropic distillation with benzene
• B. Fractional distillation
• C. Keeping over fresh CaO for few hours and then distilling
• D. Distillation under reduced pressure

Answer 1

Answer: (A), (C)

The correct options are
A Azeotropic distillation with benzene
C Keeping over fresh CaO for few hours and then distilling

Absolute alcohol can be prepared from rectified spirit by azeotropic distillation. Rectified spirit contains $95.6\%$ ethanol and $4.4\%$ water. This mixture of ethanol is known as an azeotropic mixture. Absolute alcohol is 100% pure alcohol. It is a constant boiling mixture having boiling point ${78.13}^{0}C$. The percentage of ethanol cannot be increased by using the distillation method. Because when the mixture boils the composition of the components remains the same in the vapor state. But if we change this composition by adding another component then rectified spirit can be converted to absolute alcohol by distillation method.

Here if we add lime $\left(CaO\right)$ to the rectified spirit then the water of the mixture can be absorbed by the lime. As a result, the percentage of ethanol will be changed. So the mixture will not act as an azeotropic mixture. In this way, we can prepare absolute alcohol by using the distillation method from a rectified spirit.