Question

What is the mole ratio of benzene $\left( P _{ B }^0=150\right.$ torr $)$ and toluene $\left( P _{ T }^{0}=50\right.$ torr $)$ in vapour phase if the given solution has a vapour pressure of $120$ torr?

• A. 7: 1
• B. 7: 3
• C. 8: 1
• D. 7: 8

Answer 1

Answer: (A)

$P=P_{B}^{0} x_{B}+P_{T}^{0} x_{T}$

$120=150\left(x_{B}\right)+50\left(1-x_{B}\right)$

$100 x_{B}=70$

$x_{B}=0.7$

$Y_{B}=\frac{X_{B} P_{B}^{0}}{P} \frac{0.7 \times 150}{120}=0.075 \frac{Y_{B}}{Y_{T}}=\frac{7}{1}$

$Y_{T}=1-0.875=0.125$