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Finding partial pressure with only T, V and ambient P

  1. Jun 10, 2015 #1
    1. The problem statement, all variables and given/known data
    60 L of N2 are collected over H2O at 40oC when atmospheric pressure is 760.00 torr. What is partial pressure of N2?

    2. Relevant equations
    PV=nRT
    Pt=P1+P2...

    Vapor pressure of H2O at 40oC:7.3590 KPa
    760 torr=101.3 kPa
    40oC=313oK

    3. The attempt at a solution
    PV-nRT
    (60)101.3=313(n)8.3145
    ((60)101.3)/((313)8.3145)=2.166g....That doesn't help, mass of H2O unknown.

    Pt=P1+P2?

    Pt=101.3kPa+PN...Pt is not given....doesn't work.

    Cannot assume Pt is ambient pressure because container's height affects pressure.
     
  2. jcsd
  3. Jun 10, 2015 #2
    This has nothing to do with the ideal gas law. That's just a "red herring" that they threw in to confuse you. The nitrogen has been bubbled through water, so the bubbles have come to the equilibrium vapor pressure of water at the temperature of the liquid. If the partial pressure of the water is its equilibrium vapor pressure and the total pressure is 760 mm Hg, what is the partial pressure of the nitrogen?

    Chet
     
  4. Jun 10, 2015 #3

    epenguin

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    Homework Helper
    Gold Member

    And the 60L seems also thrown in to confuse you - second question with that feature in a row.
     
  5. Jun 10, 2015 #4

    Borek

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    Staff: Mentor

    Let's face it - in the real world we are distracted by so many things, it is quite a good idea to add unnecessary information to problems just to make students learn what and when to ignore ;)
     
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