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Homework Help: Calculating Density of Oxygen at STP

  1. Sep 25, 2005 #1
    Ok, I know I have to use the ideal gas law, but am not exactly sure how to apply that to finding the density.

    PV=nRT (ideal gas law)

    1atm (volume) = n(number of moles - can I just use 1 for ease?)(8.315 J(mol•K) (temperature)

    Not quite sure where to go from here, any help would be appreciated just to get me in the right direction. Do I need the density of Oxygen at another temperature in order to do this?
  2. jcsd
  3. Sep 25, 2005 #2
    density of an element at stp is its mass/volume.
    Since-breathable- oxygen is 2 atoms at standard temp(293-298K) and pressure(1atm), you need to account for O2-- 16 grams per mole, i.e., n=2.
    Do you have the "unit" volume?
    nrt/p = V.
    you can get its atomic mass from the periodic chart.
    A decent (one bought from the college bookstore for $5.00) chart would also have the unit density on it as well.
    Hope this is helpful.
  4. Sep 25, 2005 #3
    Shortly after my post I realized that the atomic mass was the piece that I was missing, so to find n I did n=(mass)/(molecular mass), n=1gram/16, and after plugging that all in, I got a final density of 1.40 (which is basically much that of oxygen). Was I right to use n=1/16 or was it n=2? Thanks for the help.
  5. Sep 25, 2005 #4


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    Homework Helper

    The molar volume at stp is 22.4141L as I recall. This is easily calculated with the ideal gas law using 1 mole and stp, be sure to use correct units for your R. From there the density will be molar mass/molar volume.
  6. Jun 1, 2010 #5
    I found this claculation by chance and I noticed a mistake. Molecular mass for O2 is 32, not 16 because the O2 molecule is formed by two O atoms which mass is 16 each.
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