Question

At 20 ∘C the vapor pressure of benzene (C6H6) is 75 torr, and that of toluene (C7H8) is 22 torr. Assume that benzene and toluene form an ideal solution. What is the mole fraction of benzene in the vapor above the solution described in part (a)? 39 torr at 25 C

Answer 1

1 ) What is the composition in mole fractions of a solution that has a vapor pressure of 40. torr at 20°C?

Letus take x be the mole fraction of benzene in this ideal solution. Thus 1-x be the mole fraction of toluene in this ideal solution.

as we know that

(partial pressure of benzene) (mole fraction of benzene) + (partial pressure of toulene) (mole fraction of benzene)

= vapour pressure of solution
75x + 22(1-x) = 39, or:
75 x + 22- 22x = 39

53x =`17   

and x = 17 /53.

Benzene's mole fraction is 17/53 =0.32 , and toluene's mole fraction is 36/53= 0.68