Question

Rectified spirit can be converted into Absolute alcohol by distilling with?
                  (A) $NaC{O_3}$
                  (B) $Mg{(O{C_2}{H_5})_2}$
                  (C) CaO
                  (D) Both 2 and 3

Answer 1

Hint: The mixture of rectified spirit is an azeotropic mixture so to convert it into absolute alcohol what we need to do is add some substance which is hygroscopic in nature and can absorb all the water from it.

Complete step by step answer:
-First of all let us see what rectified spirit is.
Rectified spirit is a highly concentrated ethanol solution. It is also known as ethyl alcohol of agricultural origin, rectified alcohol or neutral spirits. It can be purified by means of repeated distillation, which is known as rectification.
It basically contains 55% alcohol by volume and 95.6% by mass, since the mixture of alcohol and water becomes a minimum boiling azeotrope at this concentration.
-Now we will talk about the conversion of this rectified spirit to absolute alcohol.
Azeotropic distillation of rectified spirit can convert it into absolute alcohol. We already learned above that rectified spirit contains 95.6% alcohol and 4.4% water and at this concentration it is an azeotropic mixture and is a boiling mixture with a boiling point of ${78.15^ \circ }C$. 100% pure alcohol will be absolute alcohol.
When this mixture of rectified spirit boils the composition of components remains the same in the liquid as well as vapour state and thus we cannot increase the alcohol concentration by just doing distillation. But making any changes in the composition of the rectified alcohol by mixing some other component and then doing distillation can help convert it into rectified alcohol.
-Lime or Calcium oxide (CaO) is highly hygroscopic in nature. It means that it has the ability to attract water from its surroundings through absorption or adsorption. So, when we add CaO to the rectified spirit, it absorbs all the water from the mixture. Thus changing the concentration of alcohol in the rectified spirit and now this mixture will not act as a continuous boiling azeotrope.
This is how we prepare absolute alcohol from rectified spirit.
So, the correct answer is “Option C”.

Note: Absolute alcohol (ethanol: $C{H_3}C{H_2}OH$) is highly flammable and volatile. It can be used as an alternative source of fuel and cannot be used for human consumption. But it can be used as a solvent for other industrial purposes and laboratory applications where it acts as a fuel alcohol.