Toluene in the vapour phase is in equilibrium with a solution of benzene and toluene having mole fraction of toluene 0.50. If vapour pressure of pure benzene is 119 torr and that of toluene is 37.0 torr at the same temperature, mole fraction of toluene in vapour phase will be :

Given pbenzene0  =  119  torr ; ptoluene0=  37  torrXtoluene  = Xbenzene  =  0.5(X = M.F. in liquid phase)According to Raoult’s LawPtotal =    pA0XA  +  pB0  XB               = 119(0.5)  +  37(0.5)In Vapour  phase  Applying Dalton’s Lawptoluene  = Ttotal  ×    ytoluene (Y = M.F. in vapour phase)ytoluene     =  ptoluenePtotal   =  370.51190.5  +  370.5  =  0.237