Question

When salt is dissolved in water, there is:
(A) An increase of boiling point
(B) No change in boiling point
(C) Decrease of boiling point
(D) None of the above

Answer 1

We know that boiling point is determined for only liquids substances and it is defined as the temperature at which the vapour pressure of liquid substance becomes the same as the atmospheric pressure. On reaching this temperature, the conversion of liquid molecules to the gaseous molecule (vapour phase) starts. And to answer this question, we need to know about the term colligative properties.

Complete answer:
So now we know that the boiling point of any liquid is defined as the temperature at which the vapour pressure of liquid substance becomes the same as the atmospheric pressure. On reaching this temperature, the conversion of liquid molecules to the gaseous molecule (vapour phase) starts. And to answer this question, we need to know about the term colligative properties.
Basically, colligative properties are defined as those properties of liquids which depend upon the amount of solute present in it. And one such colligative property is the elevation in boiling point.
So, when the solid substance (salt in this case) is dissolved in a liquid, the boiling point of the liquid increases.
Hence, the correct option is (A) an increase of boiling point.

Note:
We should remember that the study of elevation in the boiling point of the liquid (which is a colligative property), when a non-volatile solute is dissolved in the liquid is known as ebullioscopy. When a non-volatile solute is added, the vapour pressure of solution decreases and hence, an elevated temperature is required to reach the boiling point.