Question

The vapor pressure of benzene is 9959 Pa at 20oC, and the vapor pressure of toluene is 2973 Pa at 20 oC. A certain solution of benzene and toluene at 20oC has a vapor pressure of 6133 Pa. Find the benzene mole fraction in this solution and in the vapor above this solution.

Answer 1

according to daltons law of partial pressures.

Ptotal = P1+P2+P3 ----etc

P1,2,3 ....etc = partial pressures

Partial pressure of Benzene = Molefraction of Benzene * vapor pressure of Pure benzene

simillarly for toulene,

so that ,

Ptotal = Pmixer = Xb*Pb0 + Xt*Pt0

   Xb = molefraction of benzene = x

   Xt = molefraction of toulene = 1-x ( bcz sum of the molefractions of all components = 1)

Pb0 = 9959 pa   , Pt0 = 2973 pa , Pmixer = 6133 Pa at 20 c

   6133 = x*9959+(1-x)2973

x = 0.452

molefraction of Benzene = 0.452