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.
$n_A+n_B=\frac{78}{78}+\frac{46}{92}=1+0.5$
$P_A=P_A^0{X}_A=P_A^0(\frac{n_A}{n_A+n_B})$
$P_A=P_A^0\times \frac{1}{1.5}=\frac{75}{1.5}=50$
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.