Letter 8399

Removing tarnish from pennies 

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I'm a junior in high school. In chemisty, 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, OH, USA

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
- Gurnee, IL

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