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Temperature and mass density

  1. Jul 8, 2009 #1
    Average molecular mass of air is 29 u. What is the mass density of air at 1 atm and -50 degrees celsius??

    This is what i have so far....

    V=(NkT)/P so V= [(29u)(1.38E^-23)(-50 + 273)]/ 1 = 8.9 x10^-20

    The mass is equal to 29u x (6.022 x 10^23) =1.75 x 10^25

    density =m/v so = 1.96 x 10^44..........and that is wayyyy off! The correct answer is like around 1, 2, or 3....i need some help. What am i doing wrong?
     
  2. jcsd
  3. Jul 8, 2009 #2

    Mapes

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    Try carrying your units through your equations. What does it mean to have a molecular mass of 29?
     
  4. Jul 8, 2009 #3
    uh...i know i could try to convert the 29u to (number of atoms)...but i dont have any molecular weight
     
  5. Jul 8, 2009 #4

    Mapes

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    29u tells you something about the relationship between mass (which is connected to density) and the number of moles (which is connected to the ideal gas law that you're using).
     
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