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Q & A: Splitting Up Air

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Most recent answer: 10/22/2007
Q:
Air is made up of oxygen and nitrogen but according to a book it seems that oxygen is a little heavier than nitrogen. If you place some air in a jar and close it up how long would it take for the oxygen to settle to the bottom? Thanks.
- Cameron
Fairfax, Virginia
A:
Actually, you can't quite split up air like that. The main problem is that Oxygen and Nitrogen have almost exactly the same mass. In fact, if you took a 2 liter bottle of pure oxygen and compared it to a 2 liter bottle of pure litrogen, they would only differ in mass by .18 grams! That's really tiny. On the other hand, Helium has much less mass. That's why helium filled balloons float.

In any case, even if you wait a really really long time you won't get oxygen sinking to the bottom of a jar, even though it IS a bit heavier. The reason is that all gas atoms at normal "room" temperature are moving around so quickly, bouncing off the walls of the jar, that they stay really well "stirred up".

Adam

(published on 10/22/2007)

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