# Calculating Density of Oxygen at STP

Ok, I know I have to use the ideal gas law, but am not exactly sure how to apply that to finding the density.

PV=nRT (ideal gas law)

1atm (volume) = n(number of moles - can I just use 1 for ease?)(8.315 J(mol•K) (temperature)

Not quite sure where to go from here, any help would be appreciated just to get me in the right direction. Do I need the density of Oxygen at another temperature in order to do this?

Related Introductory Physics Homework Help News on Phys.org
Tom,
density of an element at stp is its mass/volume.
Since-breathable- oxygen is 2 atoms at standard temp(293-298K) and pressure(1atm), you need to account for O2-- 16 grams per mole, i.e., n=2.
Do you have the "unit" volume?
nrt/p = V.
you can get its atomic mass from the periodic chart.
A decent (one bought from the college bookstore for \$5.00) chart would also have the unit density on it as well.

SteveDB said:
Tom,
Since-breathable- oxygen is 2 atoms at standard temp(293-298K) and pressure(1atm), you need to account for O2-- 16 grams per mole, i.e., n=2.
Do you have the "unit" volume?
nrt/p = V.
Shortly after my post I realized that the atomic mass was the piece that I was missing, so to find n I did n=(mass)/(molecular mass), n=1gram/16, and after plugging that all in, I got a final density of 1.40 (which is basically much that of oxygen). Was I right to use n=1/16 or was it n=2? Thanks for the help.

lurflurf
Homework Helper
The molar volume at stp is 22.4141L as I recall. This is easily calculated with the ideal gas law using 1 mole and stp, be sure to use correct units for your R. From there the density will be molar mass/molar volume.

I found this claculation by chance and I noticed a mistake. Molecular mass for O2 is 32, not 16 because the O2 molecule is formed by two O atoms which mass is 16 each.