Name: Elevation in Boiling Point
Uploaded: 2019-07-19
Duration: 7 min 28 s
Description: The boiling point of a liquid is the temperature at which its vapour pressure becomes equal to atmospheric pressure. Let’s learn about the elevation in boili...

Question

Explain the effect on the boiling point and freezing point when a non-volatile solute is dissolved in a volatile solvent.

Accepted Answer

When we add a non-volatile solute like sodium chloride to a volatile solvent like water, the solute occupies a certain surface area of the solvent. As a result, the solvent molecules which are more volatile than the solute molecules get lesser opportunity to change to the vapour state. In other words, the vapour pressure of the solution becomes lesser than that of the pure solvent.
As the vapour pressure of the solvent is lowered by the addition of non-volatile solute, it is apparent that the boiling point of the solution will be higher than that of the pure solvent. In other words, the boiling point of the solvent is elevated by the addition of a non-volatile solute to it. This is known as the elevation of boiling point ( $∆ T_{b}$ ).

Similarly, due to a decrease in the vapour pressure of a solution from that of the pure solvent, the freezing point of a solution is lower than that of the pure solvent. In other words, the freezing point of the solvent is depressed by the addition of a non-volatile solute to it. This is known as depression in freezing point ( $∆ T_{f}$ ).

Explain the effect on the boiling point and freezing point when a non-volatile solute is dissolved in a volatile solvent.

Important Questions on Solutions

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