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Discussion in 'DAT Discussions' started by Lonely Sol, Apr 26, 2007.

  1. Lonely Sol

    Lonely Sol cowgoesmoo fan! 10+ Year Member

    Dec 13, 2005
    Atlanta, GA
    A sample of air held in a graduated cylinder over water has a volumne of 88.3ml at a temperature of 18.5 degree C. and a pressure of 741nm. What would the volume of the air be if it were dry and at the same temperature and pressure?
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  3. Nasem

    Nasem 2+ Year Member

    Aug 30, 2006
    Lansing, MI
    This is classic PV = nRT,
    Since n, R, and T are constancts in this, we leave them out and put

    PiVi = PfVf

    You know your initial pressure and volume,
    you also know your final pressure (since it says constant), just need to solve for Vf
  4. orthdent786

    orthdent786 Junior Member 5+ Year Member

    Dec 12, 2005
    if thats the case then Vi=Vf b/c the pressures just cancel out, i'm not sure if that is the equation we are supposed to use? maybe someone else can help?
  5. doc toothache

    doc toothache 10+ Year Member

    Jan 17, 2006
    The (vapor) pressure contributed by water at 18.5 degree C is about 20mm. It needs to be subtracted from 741mm then use P1V1=P2V2.
  6. infernobutterfl

    infernobutterfl Pyro user 7+ Year Member

    May 26, 2005
    we are supposed to know the vapor pressure of water?? o_O
  7. DentalKitty

    DentalKitty 5+ Year Member

    Mar 12, 2007
    No, I think it would be provided for you especially since VPs are temp dependent so you'd have to memorize so many. The only one I know is H2O at 100 deg C = 760mm because at the boiling point VP = atmospheric pressure. That would work for any substance at its BP and 1atm I believe.

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