Question

Which of the following statements about the composition of the vapour over an ideal 1: 1 molar mixture of benzene and toluene is correct? Assume that the temperature is constant at ${25}^{\circ }C$. (Given,vapour pressure data at ${25}^{\circ }C$. benzene = 12.8 kPa, toluene = 3.85 kPa )

• A. The vapour will contain equal amounts of benzene and toluene.
• B. Not enough information is given to make a prediction.
• C. The vapour will contain a higher percentage of benzene.
• D. The vapour will contain a higher percentage of toluene.

Answer 1

The correct option is C The vapour will contain a higher percentage of benzene.

$p_{benzene}=x_{benzene}{P}_{benzene}^0$
$p_{toluene}=x_{toluene}{P}_{toluene}^0$
For an ideal 1 : 1 molar mixture of benzene and
$tolune,x_{benzene}=\frac{1}{2}and{x}_{toluene}=\frac{1}{2}$
$p_{benzene}=\frac{1}{2}{P}_{benzene}^0=\frac{1}{2}\times 12.8KPa=6.4kPa$
$p_{tolune}=\frac{1}{2}{P}_{toluene}^0=\frac{1}{2}\times 3.85KPa=6.4kPa$
Thus, the vapour will contain a high percentage of benzene as the partial vapour pressure of benzene is higher as compared to that of toluene.