   Chapter 11, Problem 114CWP

Chapter
Section
Textbook Problem

# A solution is prepared by mixing 1.000 mole of methanol (CH3OH) and 3.18 moles of propanol (CH3CH2CH2OH). What is the composition of the vapor (in mole fractions) at 40°C? At 40°C, the vapor pressure of pure methanol is 303 torr, and the vapor pressure of pure propanol is 44.6 torr.

Interpretation Introduction

Interpretation: The composition of the vapor (in mole fractions) at 40°C for the given propanol methanol mixture should be calculated.

Concept introduction:

• Raoult's law:

The mole fraction of a solute is related to the vapor pressure of the solution thus,

Psolution=P°solventXsolvent......(1)Pisvapor pressureof the solutionsolventpressureof the solventXsolvent mole fraction ofsolvent

Explanation

Record the given data,

Mole of methanol =1.00 mole

Mole of propanol =3.18 mole

Vapor pressure of pure methanol =303torr

Vapor pressure of pure propanol =44.6 torr .

To calculate the mole fraction of methanol in liquid phase.

Totalmol=Methanolmol+Propanolmol=3.8+1=4.8mol                 χLmethanol=1.00mol4.18totalmol=0

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