Question

A solution has a 1:4 mole ratio of pentane to hexane. The  vapour pressures of the pure hydrocarbons are 20degree c are 440mmhg for pentane and 120mmhg for  hexane. The mole fraction of pentane in the vapour phase is

A) 0.200

B) 0.549

C) 0.786

D) 0.478

Answer 1

Let the pentane be 1 mole and hexane be 4 moles. 

Total number of moles of pentane and hexane in mixture = 1 + 4 = 5 mol