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Homework Help: Partial pressure question

  1. Oct 5, 2007 #1

    lzh

    User Avatar

    1) Question:
    A sample of oxygen is collected in a 172 mL
    container over water at 15C, and the barom-
    eter reads 754 torr. What volume would the
    dry gas occupy at 778 torr and 15C? Water's
    partial pressure at 15C is 12:8 torr. Answer
    in units of mL.
    2)attempt to answer:
    pv=PV
    temp constant
    (754+12.8)*172=(778+12.8)V
    V=166.779969
    I'm not exactly sure if this is the right way to do it since the question's wording is a bit confusing and there seems to be some useless information. Can anyone tell me if my answer is right here?
    Thanks
     
  2. jcsd
  3. Oct 6, 2007 #2
    you need to SUBTRACT the partial pressure of water from the first pressure of 754 torr. (wet gas to dry gas) This is now p1, v1 = initial volume. P2 is the new pressure 778. find V2
     
  4. Oct 6, 2007 #3

    lzh

    User Avatar

    thanks! i understand now!
     
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