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Vapor Pressure problem

  1. Sep 22, 2008 #1
    1. The problem statement, all variables and given/known data
    Benzene, C6H6, has a boiling point of 80 degrees Celsius. The density of benzene vapor in equilibrium with liquid benzene at 50 degrees Celsius is 1.153 g/L. What is the vapor pressure of benzene in mmHg at 50 degrees Celsius?

    2. Relevant equations
    density = m/v

    3. The attempt at a solution
    I thought PV=nRt might cover it.. substituting d=mv into the equation and getting:
    P = dRt/m
    Plugging in I get:
    [(1.153 g/L)(62.364 L Torr/mol K)(323 K)] / (1084.1 g/mol)
    P = 21.43 Torr = 0.028 mmHg

    What am I doing wrong? My professor covered what vaporization is, not how to go about getting vaporization pressure. I have a test Wednesday and I don't know how to do any of it!
  2. jcsd
  3. Sep 22, 2008 #2


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    d = m / v
  4. Sep 22, 2008 #3
    Sorry, that was a typo. I did divide when doing the actual problem. But I'm still not getting the answer. I forgot to add the choices on our homework handout.

    a) 298
    b) 50
    c) 352
    d) 462
    e) 0.392

    I still don't understand what I am doing incorrectly. Please help?
  5. Sep 22, 2008 #4


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    What are the units in the answers?
  6. Sep 23, 2008 #5


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    What is molar mass of benzene?
  7. Sep 23, 2008 #6
    The homework problem didn't give units for the answer so I have no clue. So I have no clue as to what to aim for. The molar mass of Benzene is 78.108 g/mol.
  8. Sep 23, 2008 #7
    Oh! Wow, duh, I feel stupid. I calculated the molar mass incorrectly. Haha, I've got the correct answer now! It's choice A, 298!

    haha, thanks for pointing out my mistake!
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