A solution at `20^(@)C` is composed of `1.5 mol` of benzene and `3.5 mol` of toluene. If the vapour pressure of pure benzene and pure toluene at this temperature are `74.7` torr and `22.3` torr, respectively, then the total vapour pressure of the solution and the benzene mole fraction in equilibrium with it will be, respectively:

Options

A. 35.0 torr and 0.480
B. 30.5 torr and0.389
C. 38.0 torr and 0.589
D. 35.8 torr and 0.280

Answer

C

Explanation

`x_("benzene")=(1.5)/(5)=0.3rArrx_("toluene")=(3.5)/(5)=0.7`
`p_("total")=0.3xx74.7+0.7xx22.3`
`22.41+15.61`
`=38.02~=38.0" torr "`
By Dalton's law of vapour pressure,
`x_("benzene")("vapour phase")=(0.3xx74.7)/(38)=0.589`