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Quick question on chemistry notation (mol fraction vs %)

  1. Oct 5, 2015 #1
    • Please post this type of questions in HW section using the template.
    Hi,

    I have a paper that for a gas mixture writes Ar/25%O2 implying that 25% of the atmosphere of the gas is oxygen.

    I have another paper that writes 0.02 mol frac O2 for a Ar/CO2 atmosphere.

    Please could someone tell me how I would write the 0.02 mol frac O2 in the form Ar/X%CO2 and what X would be and how you got it?

    Thanks in advance for any help!
     
  2. jcsd
  3. Oct 5, 2015 #2

    Borek

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    Staff: Mentor

    How is the molar fraction defined?
     
  4. Oct 5, 2015 #3
    hmm molar fraction is ratio of moles to moles, and to get fraction to percent you would multiply by 100, wow that was easy, sorry, thanks for the direction!
     
  5. Oct 5, 2015 #4

    Borek

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    Staff: Mentor

    Just remember composition of the gas mix - as listed - is ambiguous. 25% O2 can be v/v (more or less equivalent to molar fraction) or w/w (substantially different).
     
  6. Oct 9, 2015 #5
    hmm isnt it exactly equivalent through PV = nRT ?
     
  7. Oct 9, 2015 #6

    Borek

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    Staff: Mentor

    For real gases not so, especially when the ideal gas approximation no longer holds.
     
  8. Oct 9, 2015 #7
    Good point, thanks again.
     
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