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Tom Quackenbush wrote in
:

Salty Thumb wrote:
snip
If you take the molar density and multiply by the molecular weight, you
get the mass density.
02 1 mol / 2.74 L = 11.7 g/L
N2 1 mol / 2.74 L = 10.2 g/L
CO 1 mol / 2.73 L = 10.3 g/L
CO2 1 mol / 2.49 L = 17.7 g/L

As I mentioned in my previous post, I think those volume figures are
a little off.

According to my handy-dandy Pocket Ref, here are the densities (@
STP):

O2 1.4290 g/L
N2 1.2506 g/L
CO 1.2500 g/L
CO2 1.9770 g/L
Air 1.2928 g/L

Ha, thanks, but mine were way off. This is why I am not a chemist (or
mathematician). The correct equation is probably: v^3 - (b + RT) v^2 + a
V - ab = 0 (forgot to multiply RT by v^2 last time)

which gives
CO 1.168 g/L at 20C, 1 atm
CO 1.253 g/L at STP (using 28 for mass)

Close enough to the value you reported.

Calculations for other compounds are an exercise left to the reader