Question

In vacuum distillation, substance boils at:
A. its exact temperature
B. temperature slightly above its boiling point
C. a temperature below its boiling point
D. under high pressure

Answer 1

Hint: We know that distillation is a technique used in purification of liquid or separation of liquid components from a mixture. In this process, the liquid is heated to its boiling point to result in vapor and again condensing vapor into liquid.

Complete step by step solution:
Let’s understand vacuum distillation in detail. It is a method of distillation where the pressure above the mixture to be distilled is reduced to less than atmospheric pressure. This causes evaporation of most volatile liquids in a temperature lower than low boiling points. The principle behind this method of distillation is that boiling takes place at lower temperature than normal boiling point if the vapour pressure of liquid exceeds the ambient pressure.

So, the correct answer is Option C.

Additional Information:

The two common types of distillation used in purification of liquids are simple and fractional distillation.

In fractional distillation, a mixture consists of different substances of different boiling point is heated in a
fractional column. In this process, vapors from the boiling solution passed along a column. The temperature of the column decreases along the length and components possessing higher boiling point undergo condensation on the column and return back to solution and the component with lower boiling point passes through the column and is collected. So, the basis on which fractional distillation occurs is difference of boiling point of the components

In simple distillation, liquids are purified by bringing them to their boiling point and then collecting and condensing back to liquid. This process is useful when small impurities present in the mixture or liquids to be separated have widely different boiling points.

Note: The difference between simple and fractional distillation is, in fractional distillation, those solutions are purified where the difference of boiling points of components is not much but in simple distillation, those solutions are purified where components of the mixture have wide difference of boiling point.