At some temperature the vapour pressure of pure benzene, `C_(6) H_(6)` is 0 . 256 bar and vapour pressure of toluene, `C_(6) H_(5) CH_(3)` is 0 . 0 925 bar, if the mole fraction of toluene in a solution is 0 . 60
(i) What is the total vapour pressure of the solution ?
(ii) Calculate the composition of the vapour phase in terms of mole fraction.

Explanation

`P_A^0=0.256` bar
`x_A=0.40`
`P_B^0=0.0925` bar
`x_B=0.60`
(i) `P_A=P_A^0x_A`
`=0.256 xx0.40`
`= 0.1024`
`P_B= P_B^0x_B`
`= 0.0925 xx0.10`
0.0555
`P_("sol"^4)=P_A+P_B`
`= 0.1024 + 0.0555 = 0.1579 ` bar
(ii) `y_("toluene")=P_B/(P_A+P_B)`
`= (0.0555)/(0.158)=0.35`
`y_("benzene")=P_A/(P_A+P_B)`
`=(0.1024)/(0.158)=0.62`