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Name: Andy King
Status: educator
Age: 40s
Location: N/A
Country: N/A
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?

Thank you.

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 is H^+.

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 water,

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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