Hollow Penny Science Project

Make a hollow penny by dissolving away the zinc to leave copper metal. (United States Mint)
Make a hollow penny by dissolving away the zinc to leave copper metal. (United States Mint)

This is an easy chemistry project that uses common materials. You take a post-1982 penny, score the copper surface to expose the zinc interior, react the zinc with acid, and are left with a hollow copper penny.

Hollow Penny Materials

  • post-1982 US pennies (metal composition changed in this year)
  • muriatic acid (from a hardware store)
  • a disposable plastic container or glass jar
  • baking soda (sodium bicarbonate)
  • water

Time Required: 6 hours

Here’s How:

  1. You need to expose the interior of the pennies. You can score the edge of the pennies with a file or snip them with wire cutters, but I think the easiest way to expose the zinc is to rub the edge of each penny along a brick or concrete block. You could use sandpaper, if it’s available. Use whatever is handy to expose some of the zinc (don’t go all the way around the coin). If you can see silver metal under the copper of the penny, you’re ready to proceed to the next step.
  2. It’s best to do this step outdoors or under a fume hood, wearing gloves and protective eyewear. Read the safety precautions on the muriatic acid container. Basically, this is hydrochloric acid. Treat it with respect. Place the pennies in your container. Pour a little muriatic acid over the pennies so that they are covered. Bubbles will start to form immediately. Set the container somewhere where it will be safe from spills, children, and pets. Let the reaction proceed for about 6 hours.
  3. Carefully pour off the muriatic acid. You can wash it down a drain, providing you use a lot of water.
  4. Fill the container with water. Add a little baking soda to neutralize the residual acid.
  5. Examine your penny. The hollow penny will be a fragile copper foil.

See How to Make a Hollow Penny