What is the Mass Density of Air at 1 atm and -50°C?

[jmb07]

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?

 

[Mapes]

Try carrying your units through your equations. What does it mean to have a molecular mass of 29?

 

[jmb07]

uh...i know i could try to convert the 29u to (number of atoms)...but i don't have any molecular weight

 

[Mapes]

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).