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Name: Nathan
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: 5/29/2003


Question:
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?


Replies:
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



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