Carbonation and Titration

name         Marie
status       student
grade        9-12
location     AL

Question -   Why is it important to remove carbonation in a soda
before titrating to find the acid concentration?
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Marie,

Without looking at the procedure of your experiment it is difficult 
to tell exactly what the purpose is.  Carbonation is dissolved 
CO2.  When the carbon dioxide dissolves, it hydrogen bonds to water 
to form carbonic acid (H2CO3).  So if you are going to measure the 
amount of acid present that is not carbonic acid, then you would 
need to flatten (decarbonate) the soda first.

Matt Voss
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The carbonation itself is acidic, so it will throw off your results if
you want to find the non-carbonate acidity.

Richard Barrans
Department of Physics and Astronomy
University of Wyoming
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Dissolved carbon dioxide forms carbonic acid H2CO3. So if one is 
interested in the acidity of a soda, not counting the acidity due to 
carbon dioxide, it is necessary to separate the carbon dioxide from 
the rest of the soda. This can be done by heating the soda. Another 
way is to completely freeze the soda a couple of times because 
carbon dioxide is not soluble in ice.

Vince Calder
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Marie,

CO2 dissolved in water forms carbonic acid (H2CO3) according to the equation:

H2O + CO2 = H2CO3

Since H2CO3 has a small but measurable pKa that is higher than that 
of water, then H2CO3 contributes to the acidity of the water solution.

If in the titration you only want to know the acidity coming from 
the other acid additives (phosphoric and citric acid), then you want 
to remove the carbonation so that you do not titrate the carbonic acid as well.

Greg (Roberto Gregorius)
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Hi Marie,

Dissolved CO2 is also an acid (carbonic acid), so in fact if you 
wanted to know the true total acid concentration in a soda, it would 
be important NOT to remove the carbonation.  The difficulty of 
course is that it is quite difficult to even open the bottle without 
losing some carbonation, and it will be losing CO2 the entire 
duration of the titration, so your results would be highly variable 
unless you could perform the titration on a sealed sample 
(difficult, but not impossible).

If the point is to measure acids except for carbonic acid (e.g. 
phosphoric acid in some colas), then yes, by all means remove the carbonation.

Don Yee
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Carbon dioxide forms carbonic acid, which will contribute to the 
acid in the titration. The CO2 can usually be eliminated by heating 
the sample for a while, or by freezing it several times since CO2 is 
insoluble in ice.

Vince Calder
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