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 Calcium Carbonate vs Aluminum Hydroxide
Name: Nathan
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: 5/29/2003

We are doing an experiment on antacids in my chemistry class. Why would an antacid containing calcium carbonate be more effective than an antacid containing aluminum hydroxide?

Based solely upon the number of gm of antacid per mole of (H+) consumed, 50 and 26 gm for CaCO3 and Al(OH)3 respectively, aluminum hydroxide would be more effective. However, that may not be the only consideration. Cost, availability, and ease of formulation may also be factors. In addition, calcium is a mineral nutrient whereas aluminum [to my knowledge] is not. In fact, there have been some reports [I am not sure how reliable the studies are.] that aluminum has some undesired side effects. Another consideration is the pH at the equivalence point. A product like Alka Seltzer has a pH ~4-5 at its equivalence point -- which is on the acid side -- nonetheless it is used widely. The reason is that "acid indigestion" involves a pH of ~1-2, so it makes little practical difference whether the ending pH is ~ 4 or 7.5. The "advantage" of the dissolved antacid is that the neutralization essentially instantaneous, where the "solid" antacids could become coated with food in the stomach and slow its neutralization of the gastric acid.

Vince Calder

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 (, or at Argonne's Educational Programs

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

Argonne National Laboratory