Measuring Densities of Pennies
Background:
Today’s pennies are quite different from the penny 20 years 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, or mass per unit
of volume. In this experiment, you will determine and compare the densities of pennies minted before
1982 and after 1982, and use density data to try to identify the metal used in the core of pennies minted
after 1982.
Objectives:
In this experiment, you will:
- determine the densities of pennies minted before 1982 and after 1982,
- compare the densities of pennies minted before 1982 and after 1982, and
- try to identify the metal in the cores of pennies minted after 1982.
Materials:
25 pre-1982 pennies
25 post-1982 pennies
balance
50 mL graduated cylinder
paper towels
Procedure:
1. Work with one set of pennies at a time, either pre-1982 pennies or post-1982 pennies. 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 add 5 more pennies to those already on the balance, until you have used
all 25 pennies.
4. Fill a 50 mL graduated cylinder with approximately 20 mL of water. Be sure to use the bottom
of the meniscus to measure the water level. Record this value in the data table.
5. Still working with the same set of 25 pennies, gently drop 5 of the pennies into the graduated
cylinder. Record the new water level in the appropriate table.
6. Add 5 more pennies to the graduated cylinder, making a total of 10 pennies. Record the water
level in the table.
7. Add 5 more pennies to the cylinder and record the water level.
8. Repeat step 7 until you have added all 25 pennies to the set to the cylinder. Record the volume
after each addition.
9. Discard the water. Dry the pennies with a paper towel and either pass them to another group to
use or return them to the appropriate container.
10. Repeat steps 1-9 using the pennies in the other set of coins. Record your data in the other table.
11. Complete your data tables. Find the net volume of each group of pennies by subtracting the
initial volume of water from the total volume recorded for each group (column 3). Enter the net
volume for each group in column 4 of the data tables.
Measuring Densities of Pennies
Name: ___________________________ Date: ______________________
PD: _________
Analysis:
Number of
Pennies
Mass (g)
Pre-1982 Pennies
Total volume in
Initial volume of
cylinder (mL)
water in graduated
cylinder (mL)
Net volume of Pennies
(mL) [total volume -20
mL]
Post-1982 Pennies
Total volume in
Initial volume of
cylinder (mL)
water in graduated
cylinder (mL)
Net volume of Pennies
(mL) [total volume -20
mL]
5
10
15
20
25
Number of
Pennies
Mass (g)
5
10
15
20
25
Analysis:
1. Construct a graph of your results on separate graph paper following proper graphing rules. Let
the y-axis reflect the mass of the pennies. Plot the data for the pre-1982 pennies first. Then
draw a line of best fit (a single straight line that represents the best fit single line, may not touch
any of the data points.)
2. On the same graph, plot the data for the pennies minted after 1982. Draw the line of best fit.
3. How do the graphs compare? Describe their similarities and differences.
4. Calculate the slope of each line. (You must use x and y values that you have determined from
your line of best fit.) Remember slope is Δy/Δx or (y2 – y1)/(x2 – x1).
5. What do the values obtained for the slopes of the lines represent?
Conclusions:
1. Find the density of copper in the tables and chart section of your lab introduction packet.
Compare the density of copper with the value for the slope of the line for the pre-1982 pennies.
2. What is the density of the pennies minted since 1982? Compare the slope of the line for these
pennies with the density listed for each element in the table found in your lab introduction
packet. Which elements have a density similar to your results?
3. Which metals could be inside the copper clad pennies minted after 1982?
Measuring Densities of Pennies
Lab Checklist
1. Data tables completed
2. 2 graphs with 2 lines each
- slope calculated for each line
- axis labeled with quantity and unit
- title
- best-fit line drawn
3. A paragraph that includes all of the answers to the questions found at the end of the lab.
- how do graphs compare
- what do the slopes represent
-comparison of densities of copper and old pennies
- what metal is in the newer pennies/explain
Example of conclusion paragraph:
I did a lab to compare the density of pennies. Two graphs were created with two lines each. One line
represented the old pennies, the other line represented the new pennies. One graph was hand drawn, the
other was generated with the excel program. I thought the hand drawn graph was easier to do but it
didn’t look as nice as the excel graph. I calculated the slope for all of the lines. The slope of each of
the lines represented_____________. I compared them to the densities of common metals table. I
found the old pennies to be most like____________. I found the new pennies to be most
like___________. I think the metal in the newer pennies is ____________ because of the density values
listed in the chart and I also reasoned that even though it was close to the density for silver, it couldn’t
be silver because that is too valuable of a metal. This newer metal is less/more dense than the
_________ found in the old pennies.
Lab Grade Sheet
1. Data tables completed
______ 10 points
2. 2 graphs with 2 lines each
- slope calculated for each line
- axis labeled with quantity and unit
- title
- best-fit line drawn
______ 10 points
______ 4 points
______ 4 points
______ 2 points
______ 2 points
______ 3 points (neatness)
3. A paragraph that includes all of the answers to the questions found at the end of the lab.
- how do graphs compare
- what do the slopes represent
-comparison of densities of copper and old pennies
- what metal is in the newer pennies/explain
______ 15 points
Total 50 points