Question

What is the number of mole of benzene $(P_B^0=150torrs)$ per mole of toluene $(P_T^0=50torrs)$ in vapour phase if the given solution has a vapour pressure of 120 torrs in equilibrium with its vapour?

• A. $7$
• B. $8$
• C. $9$
• D. $10$

Answer 1

The correct option is A $7$

$P=P_B^0{X}_B+P_T^0{X}_T$

$120=150\left(X_B\right)+50(1-X_B)$

$100X_B=70$

$X_B=0.7$

$Y_B=\frac{X_B{P}_B^0}{P}=\frac{0.7\times 150}{120}=0.875$

$Y_T=1-0.875$

$=0.125$

$\frac{Y_B}{Y_T}=\frac{0.875}{0.125}=\frac{7}{1}.$