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Vapor pressure saturation

  1. Nov 15, 2008 #1
    1. The problem statement, all variables and given/known data
    "Suppose you were to collect 1.0 L air by passing it slowly thorugh water at 20C and into a container. estimate the mass of water vapor in the collect air, assuming that the air is saturated."

    I don't know where to even begin. at first i thought it had something to do with henry's law, but that didn't lead me anywhere

    2. Relevant equations
    Henrys Law
    S=kH X P
    3. The attempt at a solution
    I have no idea, I read the chapter on physical equilibria throughly, but I can't answer this question. All I need is the conceptual understanding as to how I would solve this problem. The only way I thought of doing this is
    1. find the solubility of air in water (henry's constant given)
    2. plug in the vapor pressure of water at 20C for P
    3. Obtain solubility
    4. then I have the solubility of air in water
    5. that didn't get me anywhere

    I couldn't think of anything else, conceptual guidance would be appreciated
    the answer is I don't know where to even begin. at first i thought it had something to do with henry's law, but that didn't lead me anywhere

    the answer is 0.017g
    thanks !
     
  2. jcsd
  3. Nov 15, 2008 #2

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    Apply Dalton's law of partial pressures to the vapor phase.
     
  4. Nov 15, 2008 #3
    Thanks for the reply,
    I thought about it, but still can't figure out how to do it... it shouldn't be that hard, its the first problem in the chapter!!:frown:

    so daltons law says that the total pressure is equal to the mole fractions of each species multiplied by the total pressure
    ie
    Ptot = X1P + X2P

    I have that the vapor pressure of water at 20C is 17.54
    what can I do now?
     
  5. Nov 15, 2008 #4

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    You've got volume, you've got pressure, you've got temperature. What do you know about ideal gases?
     
  6. Nov 15, 2008 #5
    wow simple
    i keep forgetting to always think about the ideal gas law
    thank you so much
     
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