tpetplyr

Alka-Seltzer also has citric acid in it which reacts with the bicarb to produce the CO2 gas that is evolved. The citric acid is a slightly stronger acid than the aspirin, and is almost certainly present in higher quantities.

The question becomes one of whether or not citric acid is strong enough to oxidize silver, and whether this reaction is even possible. My guess is that the citric acid would oxidize the silver and reduce the hydrogen to hydrogen gas. If this is the case than the cell potential for that reaction is negative, meaning it is not thermodynamically favored and will not happen spontaneously. (That is actually independant of which acid is used, as it only involves the H+ created).

For comparision, the oxidation of zinc by hydrogen has a positive cell potential, indicating it does proceed spontaneously, which we all remember from pouring HCl on it in high school chemistry. In this case the strength of the acid simply determines the rate of the reaction by determining how much H+ is present in solution.

If it was indeed the AlkaSeltzer that corroded the finish, it had to have proceeded by a different pathway, which I can't see at this moment. I'm tempted to try it with one of the old mouthpieces I have lying around.

Another little tidbit. Placing tarnished silver on aluminum foil in a bicarb solution creates another redox reaction which reduces the oxidized (tarnished) silver back to silver metal onto the surface and evolves CO2 gas while moving the sulfur (which oxidized hte silver in the first place) to the now oxidized aluminum. Good way to polish a trumpet/mouthpiece etc without worrying about removing silver. The bicarb doesn't hurt the silver here and so it won't in AlkaSeltzer either.

Stuart
3rd Year, Chemistry
Georgia Tech