Question

Benzene and toluene forms nearly ideal solution. At $20^{o}C$ , the vapour pressure of benzene is 75 torr and that of toluene is 22 torr. The partial vapour pressure (in torr) of benzene, at $20^{o}C$ for a solution containing 78 g of benzene and 46 g of toulene, is

• A. 50
• B. 25
• C. 37.5
• D. 53.5

Answer 1

Answer: (A)

Let the number of moles of benzene be n_A and that of toluene be n_B.
$n_{A}+n_{B}=\frac{78}{78}+\frac{46}{92}=1+0.5$
$P_{A}=P_{A}^{0}X_{A}=P_{A}^{0} \, \left(\right.\frac{n_{A}}{n_{A} + n_{B}}\left.\right)$
$P_{A}=P_{A}^{0}\times \frac{1}{1 . 5}=\frac{75}{1 . 5}=50$
The partial vapour pressure (in torr) of benzene, at $20^{0}C$ for a solution containing 78 g of benzene and 46 g of toulene, is 50 torr.