Question

The distillation technique most suited for separating glycerol from spent lye in the soap industry is
(a) fractional distillation
(b) steam distillation
(c) distillation under reduced pressure
(d) simple distillation​

Answer 1

Answer:

Option (c) Distillation under reduced pressure.

Explanation:

Glycerol with a high boiling point (290°C) can be separated from spent lye by distillation under reduced pressure. This process is used to purify liquids having very high boiling points. By this process, the liquid is made to boil at a lower temperature than its boiling point by lowering the pressure on its surface.

Answer 2

Answer:

(c) Distillation under reduced pressure

Explanation:

$\underline{\bold{\rm Distillation \: Under \: Reduced \: Pressure}} \\ \rm or \\ \underline{\bold{ \rm Vaccum \: Distillation}}$

Purification of high boiling points liquids and liquids which decomposes at or below their boiling points can be purified using vaccum distillation.

A liquid boils when its vapour pressure becomes equal to the external pressure. Obviously, the same liquid would boil at a lower temperature if the pressure acting on it is reduced. Since the liquid now boils at a lower temperature, its decomposition does not occur.

With the commonly used water suction pumps in the laboratory, a pressure of 10-20 mm Hg can be

obtained. Under these conditions, the boiling points are reduced by about 100 degrees. However, with vacuum pumps, pressure of the order of 0.1 mm Hg can be easily obtained.

• Glycerol which decomposes at its boiling point i.e. 563 K can be distilled/separated from spent-lye in the soap industry without decomposition at 453 K under 12 mm Hg pressure.