Question

Absolute alcohol is prepared from rectified spirit by:
A.Steam distillation
B.Fractional distillation
C.Distillation with ${\text{CaO}}$ and ${\text{Ca}}$
D.Simple distillation

Answer 1

Alcohol is a very volatile substance. Hence, we have to use that method in which very minimum or no heat is required otherwise the alcohol will evaporate.

Complete step by step answer:
Rectified spirit is a mixture of ethanol and water with {\text{95% }} ethanol and {\text{5% }} water. Absolute alcohol is pure ethanol with less than one percent water.
Let us look at each of the methods one by one and see what suits the best for separating alcohol.
Steam distillation: It is a separating process. In this process, both water and other volatile and non volatile components are taken. Stream distillation is used when the boiling point of the compound that we want to prepare is higher than boiling point of water. But in this case, it is not so. Hence, we cannot use steam distillation.
Simple distillation and Fractional distillation: They are more or less similar. Fractional distillation is used to separate two components whose difference in boiling point is lesser than ${\text{2}}{{\text{5}}^{\text{o}}}{\text{C}}$ whereas, we use simple distillation when the boiling point difference between two compounds is more than ${\text{2}}{{\text{5}}^ \circ }$. But either of them is not a good method for getting absolute alcohol. Fractional distillation is mainly used for extracting crude oils. We cannot use simple distillation because boiling point of ethanol is ${\text{78}}{\text{.3}}{{\text{7}}^{\text{o}}}{\text{C}}$ and that of water is ${\text{10}}{{\text{0}}^{\text{o}}}{\text{C}}$.
The method that can be used to extract absolute alcohol from the rectified spirit is distillation with ${\text{CaO}}$, calcium oxide and ${\text{Ca}}$, calcium. The process follows as:
Rectified spirit is poured onto ${\text{CaO}}$ and ${\text{Ca}}$. This mixture of ${\text{CaO}}$ and ${\text{Ca}}$ absorbs water and then, rest of the spirit moves to the next tray containing the same mixture. This step is repeated again and again and finally we get pure alcohol after a certain number of steps.

Hence, the correct option is C.

Note:
Absolute alcohol is ethanol. The chemical formula is ${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{OH}}$. It is a colourless liquid and is highly inflammable. It has various uses in many disciplines. In the medicinal field, it is used as an antiseptic, antidote and solvent. It is used in rocket fuel and fuel cells.