Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Chemical Reactions
Name: Andy King
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: Around 1999


Question:
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.


Replies:
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



Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory