Question
Answers

Glycerin can be purified by:
A. vacuum distillation
B. simple distillation
C. steam distillation
D. Fractional distillation

Answer
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Hint:In the method used to purify the glycerine is generally a purification technique not a separation technique as the compound gets distilled at the temperature below the boiling point temperature of the compound.

Complete step by step answer:
Vacuum distillation is a technique used for separation, when the boiling point of the compound is too high to distill the compound. There is no significant decomposition of the compound.
Simple distillation is a method used for separation of two liquids having different boiling points.
Steam distillation is the method used to purify temperature sensitive materials. Steam or water is added to the distillation apparatus and the boiling point of the compound is lowered. In this method, the component is separated at temperature below the decomposition point.
Fractional distillation is the separation technique used to separate two miscible liquids. In this repeated distillation and condensation takes place. Here the liquid mixture is separated in fractions.
Glycerin is the compound containing three hydroxyl groups with the molecular formula ${C_3}{H_8}{O_3}$. The boiling point of glycerin is 290 degree Celsius.
As the boiling point temperature of glycerin is very high and we need to purify the compound without decomposition. Therefore, vacuum distillation is used to purify the glycerine which can be done at temperature lower than the boiling point temperature.
Therefore, the correct option is A.

Note:
The glycerin is also known as glycerol which is purified by vacuum distillation at temperature 453 K and pressure under 12 mmHg.