Name:___________________________ Block:______ Date:____________________
Laboratory: Striking it Rich!
Background:
The penny, first released in 1909, was of 95% copper and 5% zinc. Today, the penny consists of 97.6% zinc and a thin copper coating. Why? In 1982, a drastic change took place to save money. The copper was worth more as scrap metal than as a one-cent coin. Why did they choose zinc? The density of zinc is almost the same as copper. Zinc is almost as hard as copper. Zinc is readily available are far less expensive. The only drawback, zinc is chemically more reactive . The solution was to coat the zinc “penny” with copper to increase durability and maintain its appearance. A silver penny could get confusing!
An alloy is a material that contains more than one element and has the characteristic properties of metals. Alloying is important because it is one of the primary ways of modifying the properties of pure metallic elements. As an example, pure gold is too soft to be used in jewelry, whereas alloys of gold and copper are quite hard. Pure gold is termed 24 karat; the common alloy used in jewelry is 14 karat, meaning that it is 58% gold (14/24 x 100%). A gold alloy of this composition has suitable hardness to be used in jewelry. Other examples are given below. In this lab, heating the penny fuses the zinc and the copper to form an alloy called brass. Brass is a homogeneous metal that varies from 60-82% Cu and from 18-40% Zn. Brass has a relatively low melting point, so the coating can be destroyed by heating the penny for too long.
Procedure:
1. Obtain three pennies, all must be dated before 1982. Record your observations of all three pennies in your data table.
2. Next, rub two of your pennies with steel wool so that all of the grime is removed and they appear to have regained their luster.
3. Prepare a 250mL beaker with approximately 200mL of tap water.
4. Using tongs (metal tipped), carefully lower the two clean copper pennies into one of the prepared heated mixtures in the fume hood. Also, bring your beaker with tap water to the fume hood.
5. Allow the penny to heat in the mixture until it has changed color. (~ 2 minutes)
6. With your tongs, remove the two pennies from the mixture and dip them into your
250mL beaker filled with water. Take the beaker back to your lab station. Next, dab both pennies on a piece of paper towel to dry and remove any access zinc.
Record your observations of the two treated pennies in your data table.
7. Select only one of the treated pennies and prepare a Bunsen/lab burner using the rubber tubing and a sparker. Carefully ignite the burner using the sparker.
8. Using your tongs, gently heat the treated penny in the burner flame. The penny should change color once again. DO NOT OVERHEAT your penny – remove it as soon as your witness a color change.

9. Using your tongs, dip the flame-treated penny in the 250mL beaker containing water and dab the penny on a piece of paper towel. Record your final observations after the flame treatment of all pennies.
10. Clean up your area, wipe off your countertops, wash your hands and return to your seat.
Data Table:
Penny (Year) Treatment Observations
1 ( )
2 ( )
3 ( )
“control”
NaOH/Zn Mixture
NaOH/Zn & Flame
Post-Lab Questions:
1. Compare the physical appearance of the three coins. What other metals do they remind you of?
2. If someone said gold was made in this activity, how can you decide whether it was or was not?
3. Name a practical use for the metallic changes you observed.
4. What happened to the copper atoms originally present in the treated pennies?
5. Why was zinc used to replace copper in pennies?
6. Do you think you could convert the treated pennies back to normal coins?
Bonus:
Answer the following question for both pre & post 1982 pennies. Must show all work.

How much is a penny really worth? o Copper cost: $2.92 / pound o Zinc cost: $0.89 / pound
- Pre-1982 Penny: 2.95 grams of copper & 0.15 grams of zinc
- Post-1982 Penny: 0.06 grams of copper & 2.46 grams of zinc
**HINT: 454 g = 1 pound