Ask A Scientist© Chemistry Archive

name         Melissa J.
status       student
age          17

Question -   Hello, my name is Melissa.  I have a chemistry question
I hope you can answer.  Does carbonation have anything to do with
acidity in soda pop?
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Yes, it does

CO2 + H2O <-> H+  +  HCO3-

The higher the concentration of CO2 dissolved in the water, the higher the
H+ concentration is (the lower the pH  or more acid)...

Don Yee
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The carbonation in soda pop originates from the addition
of carbon dioxide gas that is injected into the pop
under pressure.  The carbon dioxide gas forms carbonic
acid that creates some acidity in the pop.

Sincerely,

Bob Trach
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Hi Melissa!
    The fizz and bubbles released when most soft drinks cans are open
    are due  to carbon dioxide that was there under pression.
    The carbon dioxide  derives from carbonic acid that is very unstable,
    so...
    And thanks for asking NEWTON! Tell your friends about it!
    Mabel
    (Dr. Mabel Rodrigues)
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A little bit.  Carbonation is just carbon dioxide dissolved in water.  Some
of the carbon dioxide can combine with water to make carbonic acid,

   CO2 + H2O --> H2CO3.

The carbonic acid (present in small amounts) increases the acidity of the
pop.  However, most soda pops also contain other acids to make them sour,
such as citric acid and phosphoric acid.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
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Yes, partly. The CO2 in soda pop dissolves according to the following set
of reactions:

CO2(gas) + H2O(liq.) = CO2(aq.) = H2CO3(soln.) = H+(soln.) + HCO3-(soln.) =
H+(soln.) + CO3=(soln.)

Notice that I made a distiction between CO2(aq.) and H2CO3(soln.) This is
intentional because, although it is frequently neglected, they are different
chemical species. What is called
"dissolved carbon dioxide" is mostly CO2(aq.) and only a small amount of
H2CO3(soln.). In most discussions these are lumped together, but actually
CO2(aq.) = 650*H2CO3(soln.).
CO2 obeys Henry's law up to about 5 atm. The relation is CO2(aq.) =
0.032P(CO2).
The website http://www.sfu.ca/chemcai/pdf/c3carb.pdf gives a definitive
treatment of carbonate equilibria in water, both pure and natural.

In the  formulation of actual soda pops, sometimes phosphoric acid is used
in addition to buffer the product to a low pH ~1 to 3.
Vince Calder
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