Chemistry With Pennies

Abby Fritz and Sarena Gerber

On September 7 our Chemistry class did an experiment with pennies. We wanted to figure out how much of a penny is zinc and how much is copper. To do this we first weighed a penny made after 1982, then we cut it open to expose the inside and put it into hydrochloric acid. The acid dissolved the zinc and left the copper shell. When the reaction stopped, we washed and dried the copper shell and weighed it. From this information, we determine the percentage of copper and of zinc in the penny and estimate how much the government saves by replacing copper with zinc in its pennies.

We also made “silver” and “gold” pennies: the alchemist’s dream. We put clean pennies in a mixture of potassium hydroxide and zinc powder and heated it. The zinc dissolves in the solution and a thin layer deposits on the pennies. This makes the pennies look like they are made of shiny silver. To change them into “gold” we take the “silver” pennies and carefully heat them in the Bunsen burner flame. The layer of zinc mixes with the copper underneath and makes a brass alloy which looks like gold.

All in all it was a very “profitable” lab. Ask your child to show you their “gold” penny.