Name: Andy King
Date: Around 1999
When reacting calcium carbonate with acetic acid I realize
that you get a release of carbon dioxide gas, but I cannot seem to find a
chemical equation that explains this in detail. Could you provide one?
Dear Mr. King:
I'm happy to be able to help. This reaction is an example
of a "gas-forming" reaction. The reaction will occur upon
the treatment of any carbonate with an acid. It occurs in
2 steps, which add up to the overall reaction.
In the following notation, water is H_2O and the hydrogen cation
Step 1: acid-base reaction of acetic acid, which I abbreviate as HA, with
calcium carbonate, CaCO_3, to form carbonic acid, H_2CO_3, and calcium
acetate, CaA_2, in solution:
2HA(aq) + CaCO_3(s) ---> CaA_2(aq) + H_2CO_3(aq)
Step 2: Carbonic acid is unstable at room temperature, so it
decomposes to CO_2 and water:
H_2CO_3(aq) ---> H_2O (l) + CO_2 (g)
Sum of Step 1 and Step 2 gives the overall net reaction:
2 HA + CaCO_3 ---> H_2O (l) + CO_2 (g) + CaA_2(aq)
The formation of CO_2 tends to drive the overall reaction
by removing the product, according to LeChatelier's principle.
Very best regards,
Prof. Robert Topper
Dept of Chemistry
The Cooper Union
New York, NY 10003
Calcium carbonate = CaCO3
Acetic acid = CH3CO2H
The first thing that happens is that the carbonate (CO3--) part of calcium
carbonate is protonated by acetic acid to make carbonic acid (H2CO3).
Along with this , the calcium and acetate from calcium acetate.
2 CH3COOH + CaCO3 = H2CO3 + Ca(CH3COO)2.
In the next step, the carbonic acid breaks down to form carbon dioxide and
H2CO3 = H2O + CO2.
The overall reaction is just to sum of the two reactions given,
2 CH3COOH + CaCO3 = H2O + CO2 + Ca(CH3COO)2.
Richard Barrans Jr., Ph.D.
Chemical Separations Group
Argonne National Laboratory
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