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Where the
world gathers for metal finishing
Q&As since 1989

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Removing Tarnish from Pennies

I'm a junior in high school. In chemistry, we are doing an experiment. We placed 15 tarnished pennies into 15 different substances. Why does pepsi remove tarnish from pennies so well... along with ketchup and milk?

Jamie L.
- Parma, Ohio, USA
2001

Pepsi, ketchup and milk are cleaning the pennies because they each contain acid. Pepsi has phosphoric acid, ketchup has citric acid , and milk contains lactic acid. In effect, each is dissolving away the tarnish with their respective acids.

Dan Brewer
chemical process supplier - Gurnee, Illinois
2001

Ed. note: Please see our F.A.Q. on this subject.

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