The normal boiling point of methanol is 64.7°C. A solution containing a nonvolatile solute dissolved in methanol has a vapor pressure of 713.8 torr at 64.7°C. What is the mole fraction of methanol in this solution?

x = 0.94

Explanation:

From Raoult´s law of partial pressure in solution we know

P methanol = X methanol Pº methanol

where P methanol is the partial pressure of methanol in solution, X is the mole fraction of methanol and Pº is its pure vapor pressure.

Given the equation above we can solve for X , mole fraction:

X methanol = P methanol / Pº methanol = 713.8 torr / 760 torr

( key here is that the normal boiling point is defined as the temperature at which a substance boil at one atmosphere pressure (760 torr) which was stated in the question)

X methanol = 0.94

Explanation:

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