LEARN NC

CareerStart lessons: Grade eight

5.8 Electroplating: When is a penny worth less than one cent?

By Tammy Johnson and Martha Tedrow

Provided by CareerStart

Essential question: How do the properties of materials determine their uses?

Learning outcomes

Students will generalize the reasons that a material’s composition will determine its suitability for use in technological design.

Teacher planning

Materials needed

  • Demonstration lab materials:
    • Pre-1982 pennies (a 95% copper coin)
    • Post-1982 pennies (a copper plated coin with a zinc core)
    • Torch or butane burner
    • Non-flammable surface
    • Pie tin (for the zinc to land on)
    • Tongs (to hold the penny while being heated)
  • Student lab handout
  • Student lab materials (one set of the following for each student or pair of students):
    • 1 battery
    • 2 alligator clips
    • 1 paper clip
    • 1 toothpick
    • 1 straw
    • 1 other object of your choice (E.g. coin, clip, etc.)
    • 1 beaker with copper sulfate and water
    • Safety glasses (Essential!)

Lab safety

Students must wear safety goggles and disconnect batteries when not in use.

Time required for lesson

One class period (45 to 50 minutes)

Activities

  1. Anticipatory set: The melting penny. Demonstrate to the students how a copper penny made before 1982 can be heated and glows green, while post-1982 pennies, which have an a zinc core, melt and separate when heated. This change in the penny was an economic move to produce a cheaper coin. Both copper and zinc are malleable metals that can be plated or coated by electrolysis. This process is known as electroplating. The zinc has been copper-plated using electricity and a single displacement reaction.
  2. Describe the roles of various careers in the coin-producing process:
    • The process a chemist must use to select materials suitable for making coins and coin cores. (Physical and chemical properties of elements.)
    • The job of metallurgy in removing metals from ores to make alloys for the coins.
    • The engineer in designing a mold and press that will create the coin design desired.
    • The skilled metalworker — working with metal products in the manufacturing sector. (More information is available on the National Institute for Metalworking Skills website.)
  3. Have students complete the electroplating lab to determine which substances can be electroplated and are appropriate for use in constructing new coins. Lab procedure (explained in more detail on student lab handout):
    1. Hook the alligator clamps to the negative and positive terminals of the battery.
    2. Attach the object to be plated to the alligator clamp coming from the negative terminal test lead. (Look carefully: There is a minus sign on the negative side of the battery.)
    3. Place both alligator clamps into the liquid inside the beaker. They should not touch each other.
    4. Observe whether the object turns a different color or stays the same.

    Teacher note — information about metal ions: All metal ions have a positive charge. When you run an electrical current through a solution that has metal ions, the ions migrate or move toward the wires in the solution. In this experiment the copper ion (in the Copper Sulfate — CuSO4 ) is positive so it moves to the negative wire. Since the wire is attached to an object, the object gets copper coated with copper ions. This is the same process that is used for gold and silver-plating of metal objects.

  4. Follow-up: Discuss other items that can be electroplated and the financial implication of using precious metals over cheaper alloy cores.

Extension

Pennies made before and after 1982 also have different densities. Students can find the densities of the pennies and other coins by dividing their mass by their volume. (Volume will be determined using water displacement.)

Supplemental information

North Carolina Curriculum Alignment

Science (2005)

Grade 8

  • Goal 4: The learner will conduct investigations and utilize technology and information systems to build an understanding of chemistry.
    • Objective 4.04: Describe the suitability of materials for use in technological design:
      • Electrical Conductivity.
      • Density.
      • Magnetism.
      • Solubility.
      • Malleability.
    • Objective 4.06: Describe and measure quantities related to chemical/physical changes within a system:
      • Temperature.
      • Volume.
      • Mass.
      • Precipitate.
      • Gas production.