1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Number of moles and molecules

  1. Nov 4, 2011 #1
    1. The problem statement, all variables and given/known data
    A gas cylinder contains of 0.8 × 10^-3 m^3 volume oxygen.the temperature of the oxygen is 320k,and the pressure of the gas is 1.5 × 10^6 Pa.how to calculate:
    number of moles and molecules of Oxygen?
    mass of Oxygen if its molar mass is 32.0 × 10^-3 kg ?
    The mass of a single molecule of gas?



    2. Relevant equations

    PV = nRT → n=PV/RT

    3. The attempt at a solution
    PV = nRT → n=PV/RT
    p=1.5 × 10^6 Pa
    T=320 k
    V= 0.8 × 10^-3 m^3 = 0.8 litre.
    Is the value of the R is 0.082L atm/mol K ?
    so n= 1.5 x10^6 x 0.8/0.082 x 320

    n=5 716.46341
    is this the right way for part one?
    thanks
     
  2. jcsd
  3. Nov 4, 2011 #2

    Borek

    User Avatar

    Staff: Mentor

    You are on the right track, but R value is wrong. Please check wikipedia page on gas constant and select R value that fits all units you use. Alternatively, convert all data to units of your R constant.
     
  4. Nov 4, 2011 #3
    i am not sure,where did i go wrong?
     
  5. Nov 4, 2011 #4

    Borek

    User Avatar

    Staff: Mentor

    For example: you have pressure in Pascals, but you try to use R with pressure in atm.
     
  6. Nov 4, 2011 #5
    if i am using atm and liters, then the value of R to use is 0.082L atm/mol K ?
     
  7. Nov 4, 2011 #6

    Borek

    User Avatar

    Staff: Mentor

  8. Nov 4, 2011 #7
    n=PV/RT
    P=1.5x10^6
    V=0.8x10^-3
    T=300 k
    R=8.31
    n=(1.5x10^6 x 0.8x10^-3)/8.31x300)
     
  9. Nov 4, 2011 #8
    1200 / 2493 = 0.481347774
     
  10. Nov 4, 2011 #9
    am i on right track?
     
  11. Nov 4, 2011 #10
    the value of R=0.082 is in litre
    n=1200/24.6 =48.78
    I hope this is the right answer
     
  12. Nov 4, 2011 #11

    Borek

    User Avatar

    Staff: Mentor

    It is not about hope, it is about calculations.

    Please don't ignore units - you do it all the time:

    so you are not sure what units your answer has.

    List all the units in your calculations - see what cancels out, what is left, then you will know if what you did is OK.

    Even if I will tell you if the number you listed is right, you will still have no idea why.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Number of moles and molecules
  1. Triatomic molecule (Replies: 1)

  2. Molecule of hydrogen (Replies: 4)

  3. Diatomic molecules (Replies: 1)

Loading...