A solution at 20 o 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:

Step-by-step solution

X B e n z e n e   = 1.5 5 = 0.3 X T o l u e n e = 3.5 5 = 0.7 According to Raoult's Law P = x A P ° A   + x B P ° B P t o t a l = 0.3 × 74.7 + 0.7 × 22.3 = 22.41 + 15.61 = 38.02 ≈ 38   T o r r By Dalton's law to vapour phase Mole fraction of a gas in a mixture of gas = Partial pressure of gas P 1 Total no.moles in the mixture X B e n z e n e ′ V a p o u r   p h a s e = 0.3 × 74.7 38 = 22.41 38 = 0.589