What Metal Makes a “New” Penny?
Today’s penny is quite different from the penny of a decade ago. Before 1982, pennies were made of an
alloy of copper. Since then, they have been made with an outside coating of copper and an inner core of a
different metal. These differences in the composition of older and more recently minted pennies have
resulted in differences in the penny’s characteristics, including its density. In this experiment, you will
determine and compare the densities of pennies minted before 1982 and after 1983, and use density data
to try to identify the metal used in the core of pennies minted after 1983.
Purpose:
Determine the densities of pennies minded before 1982 and after 1983 and compare these densities to
identify the metal in the cores of pennies minted after 1983.
Pre-Lab Questions:
1.
What is the purpose of completing the graph for this lab?
2.
How should the x-axis and y-axis be labeled on your graph?
3.
What information do we need to get from the graph, in order to be able to complete this lab?
Materials:
25 pre-1982 pennies
25 post-1983 pennies
Balance
100 mL graduated cylinder
Paper Towels
Procedure:
1. Work with one set of pennies at a time, either pre-1982 pennies or post-1983 pennies. Do not use
any pennies minted in 1982 or 1983, as these were transition years and both types of pennies
were minted. Find the mass of 5 pennies from one set. Record the mass in the appropriate data
table.
2. Add 5 more pennies to the first group and obtain the mass of these 10 pennies. Record the mass.
3. Repeat step 2, each time adding 5 more pennies to those already on the balance until you have
used all 25 pennies.
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4. Fill the 100 mL graduated cylinder with approximately 20 mL of tap water. Be sure to read the
bottom of the meniscus when you measure the initial water volume.
5. Still working with the same set of 25 pennies, gently slide 5 pennies into the graduated cylinder.
Record the new volume in the appropriate table.
6. Add 5 more pennies to the graduated cylinder, making a total of 10 pennies. Record the volume in
the table.
7. Repeat step 6 until you have added all 25 pennies of the set to the cylinder. Record the volume
after each addition.
8. Discard the water. Dry the pennies and return them to their container.
9. Repeat steps 1 through 8 using the 25 pennies in the other set of coins. Record your data in the
other table.
10. Complete your data tables. Find the net volume of each group of pennies by subtracting your
initial volume recorded for each set of pennies from the total volume recorded for each group of
pennies. Enter the net volume for each group of pennies in the fourth column of your data table.
Data and Observations:
Pre – 1982 Pennies
Initial volume of water in graduated cylinder________________
Number of Pennies
Mass (grams)
Total Volume (mL)
Net Volume (mL)
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Post – 1983 Pennies
Initial volume of water in graduated cylinder________________
Number of Pennies
Mass (grams)
Total Volume (mL)
Net Volume (mL)
Analysis:
1. Construct a graph of your results. Let the y-axis represent the mass of the pennies and the x-axis
represent the net volume of the pennies. Plot the data for the pre-1982 pennies first. Then draw
the best-fit straight line through your data points.
2. On the same graph, plot the data for the pennies minted after 1983. Draw the best-fit straight
line through these data points. Be sure to include a key to identify the lines.
Post Lab Questions:
1. What is an alloy?
2. How do the lines on your graph compare? Describe the similarities and differences.
3. Find the slope of each line.
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4. What do the values you obtained for the slopes of the lines represent?
5. Find the density of copper on the table attached to this lab. Compare the density of copper with
the value for the slope of the line for the pre-1982 pennies.
6. What is the density of the pennies minted since 1983?
7. Compare the density of post-1983 pennies to the density of metals in the table attached to this lab.
What metals could be inside these copper-clad pennies?
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