The normal boiling point of methanol is 64.7°C. A solution containing a nonvolatile solute dissolved in methanol has a vapor pressure of 642.3 torr at 64.7°C. What is the mole fraction of methanol in this solution?

Answer 1

The vapor pressure of pure methanol is 760 mm at this temperature.
psolution = Xmethanol*Po
642.3 = Xmethanol*760
Then Xmethanol + Xsolute = 1
Solve for Xsolute.