Question

At ${20}^{o}C$, the vapour pressure of benzene is 70 torr and that of methyl benzene is 20 torr. The mole fraction of benzene in the vapor phase at ${20}^{o}C$ above an equimolar mixture of benzene and methyl benzene is $x\times {10}^{-2}$. The value of x (Nearest integer)

• A. 78.0
• B. 78
• C. 78.00

Answer 1

Answer: (A), (B), (C)

$P_{Total}=X_B{P}_B+X_{MB}{P}_{MB}$

$X_{MB}\text{is mole fraction of benzene in solution phase}$
$X_{MB}\text{is mole fraction of methyl benzene in solution phase}$

$Y_B{P}_{Total}=X_B{P}_B$

$Y_B\text{is mole fraction of benzene in vapor phase}$
$Y_B=\frac{0.5\times 70}{0.5\times 70+0.5\times 20}=0.7777$

$Y_B=77.77\times {10}^{-2}$

$Y_B=78\times {10}^{-2}x=78$