At 63.5 degreesC, the vapour pressure of H2O is 23.3kPa and that of ethanol is 53.3kPa. A solution is made by mixing egual masses of H2O and C2H5OH.
a. what is the mole fraction of ethanol in the solution?
b. assuming ideal-solution behaviour, what is the vapour pressure of the solution at 63.5 degreeC.
c. what is the mole fraction of ethanol in the vapour above the solution.

asked by lulu78
  1. Read this:

    posted by bobpursley
  2. thenkyou. i missed reading that pert on that page before. i knew it was something simple.
    i now have parts A and B but how do you work out C? i have the mole fraction of ethanol from part A. why is it not the same?

    posted by lulu78
  3. The mole fraction of the LIQUID is moles liquid component/total moles liquid.
    The mole fraction of the VAPOR is moles vapor component/total vapor moles. Since the vapor pressures are not the same the vapor is more concd in the more volatile component. That's one reason fractional distillation works.

    posted by DrBob222
  4. so do i use the moles i would have from part A? surely not, becayse they just give me the mole fraction of the solution.
    what do i use? i have the answer of 0.472- don't know how to get it.
    i feel so dumb and have my exam on 23rd.

    posted by lulu78

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