Copper

We learned that pennies get dull over time because the copper in the pennies reacts with the air to form copper oxide. Pure copper metal is bright and shiny, but the oxide is dull and sometimes greenish.

We dipped our dull pennies in a mixture of salt and vinegar, and the acetic acid from the vinegar dissolved the copper oxide, making our pennies brighter and shinier!

The salt served as a catalyst and sped up the chemical reaction.

Mrs. Woodard's husband drilled holes in 40 pennies, so all of our students were able to create a penny necklace as a little souvenir from our copper lesson.