Collecting CO2 Upon Release

name         Colin
status       educator
grade        6-8
location     MD

Question -   I want to measure the amount of carbonation in 
different sodas. I know the carbonation is caused by the CO2 
injected into the soda under pressure.  So, if I open the soda, I 
will lose some CO2.  If I try to keep all the other variables the 
same, do you think I can reliably measure the CO2 by shaking 
equal amounts in a graduated cylinder and measuring the volume of 
bubbles produced?  My other idea is to use the reaction between 
baking soda and the soda as an measurement of the fizz. I think 
that the baking soda will neutralize any acid and cause the 
release of CO2.   Will I really be measuring the carbonation this 
way or producing more CO2 than what was originally there?  I read 
the other answer about the balloons over the containers but I 
want to try something new.
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A relatively accurate and simple way to measure the amount 
of  carbonate present is to mix the soda with an excess of calcium 
carbonate (CaCl2) which is used in street/sidewalk de-icing 
compounds found in hardware stores. The Ca(+2) reacts with CO3(-2) 
which is in equilibrium with the CO2 to form insoluble Ca(CO3). One 
complication is that some sodas also contain phosphate salts. The 
phosphate also reacts with Ca(+2) to form
[Ca(+2)]3 [ (PO4(-3))]2. One way to avoid the interference is to 
heat the soda gently to drive off the CO2 and bubble the gas into an 
excess of CaCl2. The phosphate is non-volatile and will remain in 
the original solution.

Vince Calder
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