Question

Which of the following statements is correct for the boiling point of solvent containing a dissolved solid substance:
(A) Boiling point of the liquid is depressed
(B) Boiling point of the liquid is elevated
(C) There is no effect on boiling point
(D) The change depends upon polarity of liquid

Answer 1

Boiling point is determined only for liquids and it can be defined as the temperature at which the vapour pressure of liquid substance becomes equal to the atmospheric pressure. On reaching this temperature, the liquid molecules start converting into the gaseous molecule (vapour phase). Therefore, to answer this, we need to know about the colligative properties.

Complete answer:
We know that the boiling point of any liquid can be defined as the temperature at which the vapour pressure of liquid substance becomes equal to the atmospheric pressure. On reaching this temperature, the liquid molecules start converting into the gaseous molecule (vapour phase).
So in order to understand the change in boiling point of solvent containing a dissolved solid substance, we need to know about the colligative properties and the impact of dissolving solid substance in the solvent.
Basically, the colligative properties are those properties of liquids which depend upon the amount of solute. And one such colligative property is the elevation in boiling point.
So, when the solid substance is dissolved in a solvent, the boiling point of the liquid gets elevated.
Hence, the correct option is (B) Boiling point of the liquid is elevated.

Note:
Study of elevation in the boiling point of the liquid (a colligative property), when a non-volatile solute is dissolved in it is known as ebullioscopy. This happens because when a non-volatile solute is present, it decreases the vapour pressure of the solution and hence, more amount of temperature is needed to reach the boiling point.