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Penny Skins

What's a penny made of—copper, right? Well, yes, but there’s more to the story. Find out exactly what a penny's made of with this quick and easy lab activity. Penny Skins makes a great demo for elementary and middle school students or an intriguing hands-on activity for high school students. It meets the following National Science Education Standard for grades 5–8 physical science: Properties and Changes\ of Properties in Matter.

Materials needed

  • Burner or torch
  • 600-mL beaker
  • Pair of tongs
  • Pair of safety glasses
  • Water
  • Pre-1982 penny
  • Post-1982 penny

Safety and hazard information

Take the following safety precautions when working around a flame or any source of ignition:

  • Put on safety goggles.
  • Tie back long hair.
  • Do not allow long sleeves, cuffs, or any other part of your clothing to pass through the flame.
  • Do not touch the tongs or any other heated objects for several minutes after heating.
  • Do not perform this demo in the presence of any flammable materials, liquids, or vapors.

Procedure

Review the figure below before you begin.

  1. Put on safety goggles, tie back long hair, and secure any loose articles of clothing that might contact the burner.
  2. Grasp a post-1982 penny with the tongs and heat it in the flame of the burner.
  3. Hold the penny over the beaker when the core starts to separate (this usually takes 2–3 minutes). Gently shake the penny as it melts to remove its molten core.
  4. Drop the penny skins into the beaker and allow them to cool.
  5. Remove the cooled penny skins and core from the beaker. Dry them and put them in a labeled plastic bag. Pass the bag around the room.
  6. Grasp a pre-1982 penny with the tongs and heat it in the flame of the burner. What happens?
  7. Drop the penny into the beaker and allow it to cool.
  8. Remove the cooled penny from the beaker. Dry it and place it in a labeled plastic bag. Pass the bag around the room.

Disposal

Pour the water down the drain. Wrap the penny skins and zinc core in paper before discarding them in the trash.

What is happening?

Before 1982 copper was the primary component of a penny. Late in 1982 the composition of a penny was changed.

  • 1962–1982: 95% copper, 5% zinc
  • 1982–present: 97.5% zinc, 2.5% copper

Melting points

Copper has a much higher melting point than zinc does. As you saw in the demo, the heat of the burner flame was hot enough to melt the zinc, but not the copper. If you watched the flame closely, you saw the characteristic blue-green color that copper emits during a flame test.

Alternative demo

Copper has a much higher melting point than zinc does. As you saw in the demo, the heat of the burner flame was hot enough to melt the zinc, but not the copper. If you watched the flame closely, you saw the characteristic blue-green color that copper emits during a flame test. Just want to show your students that the pennies are different on the inside? Then cut open a pre-1982 penny and a post-1982 penny with a pair of heavy-duty clippers. Put each penny in a separate labeled bag, and pass them around for your students to see.

To learn more about coins or currency visit these Web sites:

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