Ask A Scientist Chemistry Archive

Question:
The solubility of a gas increases with pressure, but does the solubility
of a CO2 solution increase when you increase the pressure of nitrogen and
oxygen over the solution?  I saw something in the store which is a pump
that you screw onto a pop bottle.  You then pump it up to maintain the 
pressure and supposedly the fix fiz in the bottle.  Does this work?  If so
why?  Why should more nitrogen over a gas cause more CO2 to stay in 
solution?  Why should nitrogen affect the equilibrium of the CO2?
 mark linnerud

Answer:
You're pumping air into the bottle right?  And air is made of nitrogen
and oxygen.  So there is where your dilemma is?  The nitrogen and oxygen
aren't affecting the solubility of the CO2, it's the pressure of the
gases over the liquid.  You said it in the first line of your question.
Maybe I'm not understanding what you're trying to ask.  When you open a
can or bottle of pop, beer, etc. for the first time you release the 
pressure that was in the container.  The pressure was caused not only by
CO2 but also air (aka O2 and N2).  The CO2 then comes out of the liquid
because of the decreased pressure.  Hmmm, repost if you're not getting
my point.
-joe