At 20°C the vapor pressure of benzene (C6H6) is 75 torr, and that of toluene (C7H8) is 22 torr. Assume that be

Question

(a) What is the composition in mole fractions of a solution that has a vapor pressure of 43 torr at 20°C?
(b) What is the mole fraction of benzene in the vapor above the solution described in part (a)?

Answer 1

Assuming a linear pressure distribution law, This means no bonding between the two liquids:
Let x be the Mole fraction of benzene;
so (1-x) is Mole fraction of the toluene

x * 75 + (1-x) * 22 = 43 torr
53x = 21
x = 21/53 = 0.4

So 40% is benzene and 60% toluene