Question: Why can Coca-Cola be used to clean rust?

This question always made me a little nervous and is one of the reasons why soda is still a last resort for caffeine for me. I mean, if Coca-Cola can be used to clean up rust, what on earth is it doing to your teeth?

Luckily the MythBusters answered one of the questions — they left a tooth in a jar of cola overnight and it came out intact. But, what people often forget from that episode is that Adam and Jamie decided cola was not a good resource for cleaning rust.

Norbert Pienta, a professor of chemistry at the University of Georgia, said he had never tried using Coca-Cola to clean rust before, but that what happens is a chemical reaction caused by the phosphoric acid in the soda. It’s a common ingredient in many industrial tarnish and rust removers.

“If you know anything about the structure of rust — so iron oxide — if you exchange the oxide with phosphate, I think you go from something that’s bright orange to something that’s not as colorful. So, one of the mechanisms may simply be that the rust is there but you don’t see it because it’s not colored.”

That’s the same process that’s pointed out in this video by the American Chemical Society at 2:04. The iron oxide is turned into ferric phosphate by the phosphoric acid. So it doesn’t go away, per se, it just gets darker and easier to remove.

Pienta said it although phosphoric acid can be found in both soda and industrial cleaners, it wouldn’t make much sense for a soft drink company to use something with the same strength as the other because people have to be able to drink the product safely.

He also said people forget the mechanical aspect of removing rust — you’re going to have to scrub it off.

“People have suggested that if you remove baking soda that you can also remove rust,” he said. “Well that’s in the opposite direction because that’s a base and the other one, Coke, is an acid so how could both of those work? What’s likely that’s happening with baking soda is it’s the powder. It’s the paste. The grit of it, if you will, is the part of it that’s removing the surface part of it.”

The Mythbusters did find cola was good for cleaning the tarnish off pennies, though. And if you want to put that in your stomach on a regular basis, that’s your own business.