Name: Solid Solutions
Uploaded: 2019-07-19
Duration: 2 min 56 s
Description: Solutions can be categorized as solid, liquid, and gaseous based on the physical states of solvents and solutes. In this video, let's learn about solid solutions.

Question

Show that the relative lowering of vapour pressure is a colligative property.

Accepted Answer

Relative Lowering of Vapour Pressure:- On dissolving the non-volatile solute in a pure solvent, the vapour pressure of a pure solvent gets gradually decreased.

Let us assume that $P^{0}$ is the vapour pressure of the solvent and $P_{s}$ is the vapour pressure of the solution, then the lowering of vapour pressure can be written as $(P^{0} - P_{s})$ . This lowering of vapour pressure relative to the vapour pressure of the pure solvent is called the Relative lowering of Vapour pressure. Thus,

Relative lowering of vapour pressure $=$ $\frac{(P^{0} - P_{s})}{P^{0}}$

According to Raoult's law, $\frac{(P^{0} - P_{s})}{P^{0}} = \frac{n}{n + N}$

where, $n =$ number of moles or molecules of solute.

$N =$ number of moles or molecules of solvent.

The above equation gives the relative lowering in vapour pressure which is equal to the mole fraction of the solute. Hence, relative lowering of vapour pressure is a colligative property.

Show that the relative lowering of vapour pressure is a colligative property.

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