A solution contains a mixture of pentane and hexane at room temperature.?

A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 251torr . Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature. What is the mole fraction of hexane?

For the solution, the vapor pressure of the solution will equal the sum of the individual vapor pressures. Each component’s vapor pressure is equal to the vapor pressure of the pure solvent multiplied by that components mole fraction in the solution:
Psol = P(pentane)X(pentane) + P(hex) X(hex)
Let m = mole fraction of hexane. 1-m will equal mole fraction of pentane. So,
251 = 425 (1-m) + 151 m
251 = 425 – 425m + 151 m
-174 = -274 m
m = 0.635 = mole fraction of hexane

Hexane Pentane

Leave a Comment