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=90 (was molecular weight of dry air)



Sorry for asking after the thread is over. Is
it only me who sees, for example, that the
percentage of the N2 in air is =0978.084?
I suppose that the =09 was automatically
inserted (in each numerical line) as the
message was processed over the Internet.
I do not think that my computer did this.
Ludwik Kowalski

On Wednesday, May 12, 2004 Robert Cohen wrote:

I'm trying to determine the molecular weight of dry air and
the during the procedure (which I seem to be doing right)
I've raised a couple of questions that I can't answer.

First, some background: As I understand it, the molecular
weight of dry air is the average mass per mole of all of
the various molecules that make up dry air. The percentage
of each molecule type is given as:

N2=0978.084
O2=0920.9476
Ar=090.934
CO2=090.0314
Ne=090.001818
He=090.000524
CH4=090.0002
Kr=090.000114
Xe=090.0000087

The average mass per mole of each type is determined by
using the above percentages with the atomic weight of each
type. The atomic weight is determined by averaging the
mass per mole of each isotope based upon the relative
abundance of the various naturally-occuring isotopes.

What I want to know is:

1) Can the isotope distribution of molecules like N2 and O2
be determined the isotope distribution of the elements N
and O? For example, if 16O, 17O and 18O have relative
abundance of 99.757%, 0.038% and 0.205%, would 32O2, 34O2
and 36O2 also have an abundance of 99.757%, 0.038% and
0.205%? If so, why? Couldn't there also be a 33O2?

2) Is the relative abundance of the isotopes of a given
element the same for air as for any other material? For
example, is the relative abundance of CO2 isotopes the
same for gaseous CO2 as for solid CO2? If so, why?

____________________________________________________
Robert Cohen; 570-422-3428; www.esu.edu/~bbq
East Stroudsburg University; E. Stroudsburg, PA 18301