A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 252 torr . Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature.

Question

A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 252 torr . Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature.
What is the mole fraction of hexane? (Assume ideal behavior.)

DrBob222 · Answer

phex = Xhex*Pohex
ppen = Xpen*Popen

eqn1 Then Xpen = 1-Xhex
eqn2 phex + ppen = 252

Substitute and solve these two equations for Xhex and Xpen.
I worked through them and got about 0.4 for pentane and about 0.6 for hexane. Post your work if you get stuck.