Question

The vapor pressures of benzene, toluene and ortho xylene are 75 torr, 22 torr and 10 torr at ${20}^{o}C$. Which of the following is not a possible value of the vapor pressure of an equimolar binary/ternary solution of these at ${20}^{o}C$? Assume all form ideal solution with each other.

• A. $48\frac{1}{2}$
• B. $16$
• C. $35\frac{2}{3}$
• D. $53\frac{1}{2}$

Answer 1

The correct option is D $53\frac{1}{2}$

In the equimolar binary mixture, the mole fraction of two components will be 0.5 each.
When different equimolar binary mixtures are formed, the total pressure is as calculated below.

$P_T=\frac{1}{2}(75+22)=48.5torr$
$P_T=\frac{1}{2}(75+10)=42.5torr$
$P_T=\frac{1}{2}(22+10)=16torr$

In the equimolar ternary mixture, the mole fraction of two components will be 0.33 each.
When the equimolar ternary mixture is formed, the total pressure is as calculated below.

$P_T=\frac{1}{3}(75+22+10)=35\frac{2}{3}torr$

In all these case the value $53\frac{1}{2}$ is not obtained.

Option D is correct.