Why does indigestion medicine contains Citric Acid?

Answer 1

Citric acid is a mild acid, and sodium bicarbonate is a mild base. When you combine the two in H2O, the acid reacts with the bicarbonate releasing carbon dioxide gas (and I think forming sodium citrate) and neutralizes the solution. This gas is the "fizz-fizz" that follows the "plop-plop" in the Alka-Seltzer ad, and it is the reason why it is called Alka- SELTZER. I'm not a chemist, but I suspect the sodium citrate is a harmless byproduct rather than a useful medicine. Sodium citrate is mostly used as a chelate or antioxydant in prepared foods and medications.

By the way, the active ingredient in this formulation is 325 mg aspirin. I'm not sure how aspirin helps indigestion since it irritates a lot of people's stomachs. But I think the idea behind the acid/base reaction is to have some of that fizz enter the stomach where it will become trapped eventually causing you to belch.

Answer 2

Alka-Seltzer Effervescent Antacid contains citric acid, which buffers the sodium bicarbonate solution so that it's not as strongly alkaline (and which also helps to create the fizz).

http://www.healthguidance.org/entry/9854/1/Indigestion-and-Antacids.html