That makes sense, thanks for the explanation.

(Kelly E Jones) wrote in
:

In article ,
Salty Thumb wrote:

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

True!


Assuming the numbers are right, oxygen has more mass density than
carbon monoxide (but slightly less particle density). For purposes of
asphixation, the CO vs O2 comparison is what matters.

Not really... O2 and N2 don't separate out - they form, effectively, a
'solution', so the density of 02 is not really relevant. It's the
density of 'air' which matters, which is between the density of air
and nitrogen (and closer to nitrogen).

I still can't work out how mass density is relevant when talking about
gases

Because mass density, coupled with gravity, is what causes bouyancy.

or how adding atomic weights can give a correct indication of
density or buoyancy.

Because for most gases (at fixed temperature and pressure), the molar
volume (molar density) is roughly constant, thus the molecular weight
is a good indicator of the mass density, which determines bouyancy.

If we say that a mole of any gas occupies roughly 24 liters at STP,
and a mole of gas weighs it's molecular weight in grams, then the
density of any gas is proportional to it's molecular weight. The
density of CO2 is thus about 44 grams per 24 liters.

It would be akin to saying water floats on oil
(obviously it doesn't), because water (1 + 1 + 16 = 18) is lighter
than oil (say minimum of 2 H and 2 C = 26).

No, gases and liquids are vastly different phases. The molar volume
of most gases (at STP) is roughly the same; the molar volume of
liquids can be orders of magnitude in difference.


To me it makes more sense (when talking about gases at least) to
talk about particle density

Nope, not at all. Gravity doesn't care at all about particles, it
only cares about mass...

Kelly