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Fri 24 Dec, 2004 06:04 am
Does oxygen actually weigh anything?
Is an oxygen cylinder more heavy when it is full?
Re: oxygen
Patricia Holland wrote:Does oxygen actually weigh anything?
Is an oxygen cylinder more heavy when it is full?
The weight of oxygen is 32u per molecule, and 16u per atom.
Yes and Yes.
What Einherjar is saying is that approximately
623,000,000,000,000,000,000,000 molecules of oxygen weigh 32 grams. That big number is called Avagadros number and is the number of atoms we use a a standard for figuring out weights (i.e. masses for the scientifically correct).
But the simple answer is that if you put an empty cylinder and a full cylinder on a scale, the full cylinder will weigh a bit more. This of course assumes that the "empty" cylinder is completely empty (i.e. a vacuum). If the empty cylinder contains air, then all bets are off.
Air has its own weight.
And a pressurized full oxygenbottle would weigh more than one containing non pressurized air.
What form does pure nitrogen take by the way? N2? N3?
Re: oxygen
Einherjar wrote:Patricia Holland wrote:Does oxygen actually weigh anything?
Is an oxygen cylinder more heavy when it is full?
The weight of oxygen is 32u per molecule, and 16u per atom.
One question: What does "u" stand for?
"u" is the atomic mass unit, equivalent to 1/12 of the mass of an atom of Carbon-12.
Einherjar wrote :
Quote:What form does pure nitrogen take by the way? N2? N3?
As a molecule of nitrogen is composed of two atoms, hence it's form is N2.
Francis wrote:As a molecule of nitrogen is composed of two atoms, hence it's form is N2.
Then oxygen is heavier than air as well, at equal pressure.
Oxygen 32u, air is 29u or 27u?
Oxygen 32u, Nitrogen 28u, Argon 40u.
Googled composition of air and came up with this:
Composition of air
I knew air was 21% oxygen and 78% nitrogen, so I figured I'd be safe claiming Oxugen was lighter than air.
unable to be wrong
But you know 21% and 78% are both by volume. Calculating by them are improper.
^JB^ wrote:unable to be wrong
But you know 21% and 78% are both by volume. Calculating by them are improper.
Not really, gasses take up space proportional to their number of molecules, so percent by volume equals percent by ppm.
^JB^ wrote:GOD i am confused!
I'll try to clarify.
A given number of molecules of any gass will at any one temperature temperature and pressure take up the same amount of space as the same number of molecules of any other gass or mixture of gasses under the same conditions. Thus proportion in volume is the same as proportion in molecules.
Calculating using weight per molecule (32u, 28u, 40u) and proportion in molecules (equal to proportion in volume) is not improper.
Nice, I see
But honestly your first paragraph is too hard for me to undertand
Still not correct calculating by percentages.
Quote:Calculating using weight per molecule (32u, 28u, 40u) and proportion in molecules (equal to proportion in volume) is not improper.
Depends on what you are trying to calculate. If you are trying to determine what how much weight of each element is in an air sample, then yes, you would use the weight proportions and the atomic masses. If you want to know which gas is heaviest, then you only need the atomic mass units. One mole of O2 takes up the same space as one mole of N2, but the O2 weighs more, so O2 is more dense at standard temperature and pressure than N2. O2 is heavier than N2.
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