Turning Copper Pennies Golden
Procedure adapted from Flinn
Concepts: oxidation-reduction reactions, alloys
Materials per pair: TWO (2) Clean pennies
1g granular zinc
25-mL 1M ZnCl2 (aq)
Distilled H2O
Balance
2 100-mL glass beakers
50-mL graduated cylinder
Tongs or forceps
Hot plate
Paper toweling
Procedure:
1. Find the mass of each of your pennies before starting the lab
2. Add 20-mL of distilled water to one of the beakers
3. In the second 100-mL beaker, mix the granular zinc with 20-mL of zinc chloride solution.
4. Heat the Zn-ZnCl2 mixture on a hot plate set to medium.
5. Carefully and gently heat the mixture until the solution boils.
6. Using tongs, immerse the pennies into the mixture until the coins appear silver.
7. Use forceps to remove the pennies and dip them into the beaker with distilled water.
8. Shine the silvery pennies with paper towels.
9. Use tongs to place ONE of the silvery pennies onto the hot plate and heat gently until the
penny turns golden. Turn the coin using tongs.
10. When both sides of the coin are golden, dip the golden coin into the first beaker (distilled
water) to cool for several minutes.
11. Find the mass of both coins after being treated.
Data:
Penny 1 “silvery”
Penny 2 “golden”
Mint date
Mass BEFORE plating
Mass AFTER plating
Mass Zinc added
Analysis Questions:
1. What kind of alloy was made in this experiment? How do you know?
2. What is the % composition of the coins used in this experiment according to the U.S. Mint?
3. What is the % composition of the “counterfeited” silver and gold coins produced in this
experiment?
4. What kind of plating was used in this experiment: surface or displacement? Explain your
thinking.
5. Examine this series of chemical equations and notes. What is happening in each reaction:
oxidation, reduction or something else? Match each chemical equation to a step in the
procedure. Explain your thinking.
6. Write a conclusion paragraph that
a. Explains the difference between oxidation and reduction
b. Describes your thoughts about the chemical processes observed in the experiment
c. Provides insight into at least two other properties that can be used to fight against
counterfeit coins