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Homework Help: Molar mass of gas X pls help

  1. Oct 28, 2006 #1
    the mass of a 250cm3 round bottomed flask is filled with gas X is determined to be 16.2850g. the mass of the empty flask and stopper is 15.9516g. what is the molar mass of gas X?

    am i right to do it this way:

    mass of gas X alone = 16.2850 - 15.9516 = 0.3334g
    volume of gas X = 250/1000 = 0.25 dm3

    molar mass of gas X = 0.3334/0.25 = 1.3336g/dm3

    however, the answer is 32g, where did i make a mistake?

    thank you
  2. jcsd
  3. Oct 28, 2006 #2
    what conditions are you working under?? STP?

    molar mass= g/mol
    not g/L

    If its at room temp then you have:
    1 atm
    24.2 L/mol

    .250L/(24.2L/mol)= .01033mol

    .3334g/.01033mol= 34g/mol
    Last edited: Oct 28, 2006
  4. Oct 29, 2006 #3
    working under rtp

    thank you
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