The vapour presssures of pure benzene and toluene are 160 and 60 mm Hg respectively. The mole fraction of benzene in vapour phase in contact with equimolar solution of benzene and toluene is

Options

A. 0.073
B. 0.027
C. 0.27
D. 0.73

Answer

D

Explanation

Pure benzene vapour pressure `=160 mm` of Hg
Pure toulene vapour pressure =60 mm of Hg
`X_(B)=X_( T) =0.5`
`rho_(B)= X_(B) xx P_(B)^(0)=0.5 xx 160 =80 mm`
`rho_(T)=X_(T) xx P_(T)^(0)=0.5 xx 60 =30 mm`
`rho _("Total")=80+30=! 10 mm`
Mole fraction of benzene in vapour phase,
`=(rho_B)/(rho_"Total")=(80)/(110)`
`=0.727 approx 0.73`.