[UG]

Hey, I've got a question:
How do I calculate the density of air given that it is 80% Nitrogen and 20% Oxygen and at temperature 300K and pressure 101325 Pa.
I went and found the partial pressures of each gas,
P_N2 = 81060 Pa
P_O2 = 20265 Pa
Then I rearranged the ideal gas law, substituting n=m/M and getting p= mRT/MV which simplifies to p=d(ensity)RT/M
I then calculated the density of each individual gas:

d_O2 = 20265 x 0.032 / 8.314 x 300
= 0.26 kg m^-3
d_N2 = 81060 x 0.028 / 8.314 x 300
= 0.91 kg m^-3

Is this right? If so, how can I find the density of a mixture of the two gases? Just average them?

[AWK]

Use mean molecular mass of air (0.8x28+02x32)=28.8 and put into your eqation for density.
But from your calculation the density is just a sum of two numbers 0.26+0.91

[billnotgatez]

I know it is interesting to compute it yourself but it is nice to know the result so you can see how close you came

from Googleing

Total Molecular Mass of Air     28.97
At IUPAC standard temperature and pressure (0 °C and 100 kPa), dry air has a density of 1.2754 kg/m3.

The above is for clean dry air

several sites discuss the effect of water vapor

[UG]

Okay, thanks!