How to Make a Hollow Penny

This is a cool experiment to use on your worthless pennies. It's a cool trick to show your friends and teachers, so just round up all your useless pennies!


  1. 1
    File off a side of the penny with sandpaper, wire cutters, a file, etc.. It doesn't matter what you use, as long as the interior is exposed; this step isn't essential, but the end result will be more obvious.
  2. Image titled Make a Hollow Penny Step 2
    Place the penny in the bottom of a clean empty glass container. If you want to do more than one penny, then you may wish to space them evenly apart.
  3. Image titled Make a Hollow Penny Step 1
    Pour a small amount of Muriatic acid (hydrochloric acid) into the container, just enough to cover the penny plus half an inch. The penny will bubble as the zinc center reacts with the acid, leaving the paper-thin copper "jacket".
  4. Image titled Make a Hollow Penny Step 3
    After 6 hours, or once the acid solution stops bubbling, pour the acid off slowly into cold running water. Be sure the amount of water is much greater than the amount of acid, so you don't damage your pipes, and don't let the penny go down the drain!
  5. Image titled Make a Hollow Penny Step 4
    Fill the jar with water and a little baking soda to neutralize any remaining acid.
  6. 6
    Thoroughly rinse the penny, being careful not to damage the fragile shell.


  • If you feel that muriatic acid is too dangerous, then you can just mix salt with vinegar for a far weaker form of the acid. It will take a couple more days for your penny to hollow out if you choose to use salt and vinegar.
  • Muriatic acid can be bought at the hardware store; it's used for cleaning concrete.
  • Make sure to use a glass container, because glass won't react with the acid.
  • You can do more than one penny at a time, but you'll need more acid.


  • Never pour water into acid.
  • Never mix other chemicals with Muriatic Acid- you may create an explosive substance.
  • Muriatic acid (HCl) can burn your skin and eyes, so use proper precautions and safety equipment to protect yourself. (Gloves, safety glasses, and long sleeves at least)

Things You'll Need

  • Goggles
  • Disposable glass jar
  • Muriatic acid
  • Post-1982 penny (mostly zinc, barely any copper)
  • Rubber\latex gloves
  • Baking soda
  • Water

Article Info

Categories: Science for Kids