Question

The vapour pressure of a pure solvent at T K is 608 torr when a non-volatile solute is added to, the vapour pressure of the solution dropped to 456 torr. The mole fraction of the solvent in the solution is:

• A. 0.5
• B. 0.25
• C. 0.75
• D. 0.1

Answer 1

The correct option is C 0.75

Let the solvent be A and the non-volatile solute added be B.

Now, we know that,$PV=nRT$(gas law equation)

Therefore,$P\propto n$

$\Rightarrow P_A\propto n_A$$\to \left(1\right)$

Also, $P_B\propto n_B$$\to \left(2\right)$

And, adding equations (1) and (2) , $P_{Total}\propto n_{Total}$$\to \left(3\right)$

Now, dividing equations (1) and (3), we get $\frac{P_A}{P_{Total}}=\frac{n_A}{n_{Total}}=molefractionofA$

$=\frac{456}{608}=0.75$

Hence, option (c) is the correct answer.