The Density of Pennies
The Composition of the Cent
From the US Mint: (http://www.usmint.gov/about_the_mint/fun_facts/?action=fun_facts2_)
Following is a brief chronology of the metal composition of the cent coin (penny):




The composition was pure copper from 1793 to 1837.
From 1837 to 1857, the cent was made of bronze (95 percent copper, and five percent tin and zinc).
From 1857, the cent was 88 percent copper and 12 percent nickel, giving the coin a whitish appearance.
The cent was again bronze (95 percent copper, and five percent tin and zinc) from 1864 to 1962.
(Note: In 1943, the coin's composition was changed to zinc-coated steel. This change was only for the year 1943 and was due
to the critical use of copper for the war effort. However, a limited number of copper pennies were minted that year.

In 1962, the cent's tin content, which was quite small, was removed. That made the metal composition of the cent
95 percent copper and 5 percent zinc
The Problem:
The US Mint, once again, changed the composition of the penny from mainly composed of copper to
97.5 percent zinc and 2.5 percent copper (copper-plated zinc). When did this happen? (This can be
determined by finding the density of the pennies as Copper has a density of 8.96 g/cm 3 and Zinc has
a density of 7.13 g/cm3.)
Hypothesis Question: In which decade (1960’s-2010’s) did the US Mint change the composition of
the Penny?
If the Penny composition was changed in the __________ then the density of the pennies would
_____________________________________________________________________________.
Skills:
Measure mass and volume
Calculate density graphically
Graph and analyze data
Materials:
Sets of 20 pennies from the 1960’s,
70’s, 80’s, 90’s, 2000’s, 10’s
50 ml Graduated cylinder
Beaker
Created by V. Anderson 2013-2014
Paper Towel
Balance
Graph paper
Procedure:
1. Procure a set of pennies from one of the decades to be studied.
2. Group the pennies into 4 groups of 5 pennies.
3. Use the balance to find the mass of one stack of 5 pennies. Record mass on
your data table.
4. Then find the mass of 10, 15, and 20 pennies. Record each mass on your table.
5. Fill the graduated cylinder with around 20 ml of water.(be sure to read the
meniscus to check your volume.) Record initial volume.
6. Add 5 pennies to the water. Record the new volume.
7. Add 5 more pennies for a total of 10, and record the new volume.
8. Continue adding 5 pennies until you have the volume for 15 and 20 pennies
recorded.
9. Calculate the actual volume of each set of pennies by subtracting the initial
volume of water from the final volume of water and pennies.
10. Dry the pennies before returning them to the Penny area.
11. Repeat the process with each of the sets of Decade Pennies.
12. Be sure to clean up when you have completed the activity.
Created by V. Anderson 2013-2014
Data Table:
Volume (mL) in
water
Volume (mL) of
Pennies only
10's
Mass (g)
Volume (mL) in
water
Volume (mL) of
Pennies only
2000's
Mass (g)
Volume (mL) in
water
Volume (mL) of
Pennies only
90's
Mass (g)
Volume (mL) in
water
Volume (mL) of
Pennies only
80's
Mass (g)
Volume (mL) in
water
Volume (mL) of
Pennies only
Mass (g)
70's
Volume (mL) in
water
Volume (mL) of
Pennies only
# of Pennies
Mass (g)
60's
0 (initial
Volume of
water)
5
10
15
20
Analysis:
1. On your graph paper, set up your x axis to represent the Volume(mL) and your
y axis to represent the Mass(g)
2. Plot the points for mass and volume of the 1960’s pennies for 5, 10, 15, and 20
pennies.
3. Using a straight edge, draw the best fitting straight line through the points.(DO
NOT CONNECT THE DOTS) The line must begin at (0,0).
4. Using a different color for each decade, repeat steps 2 and 3 for each of the
decades
5. Using the formula:
Slope = y2-y1
X2-X1
(mass)
(volume)
Calculate the average density of the pennies based on decade where y is mass
divided by x as volume.
Questions:
1. Which decade(s) had the greatest density?
2. Which decade(s) had the lowest density?
3. In Which decade do you see a distinct change in the density of the pennies?
Created by V. Anderson 2013-2014
4. If you were asked to determine the actual YEAR that the composition of the
pennies changed, how would you go about doing this? What procedures would
you follow? What materials would you need? How would you analyze your
data? (write this out like a lab worksheet.)
Conclusion:
Write a full, formal, lab report for this experiment. Remember the sections are
as follows: (this must be typed—12 font, double spaced—when you turn it in.)
I. Title page
a. Title
b. Author’s name
c. Team-mates’ names
d. Teacher name(s)
e. Class period
f. Date
II. Introduction
a. The problem/question
b. Background Information
c. Hypothesis (testable—if/then type statement)
III. Methods
a. Materials
b. Step-by-step procedures
c. (key question for analyzing this section: Could a stranger pick up your
paper and successfully recreate what you did in lab?)
IV. Results / Data
a. Report data (charts)
b. Analyze data (describe the information found in the charts)
c. Is this data consistent with the hypothesis? (yes or no)
d. Graphs
i. Graphs and charts are properly labeled and titled.
ii. Graphs are neat, professional, and contain all key components.
V. Discussion
a. Discuss results in terms of the original problem
b. Use the data to support your conclusion
c. Include broader meaning/application/real world integration.
d. Was your hypothesis proven or disproven by your data/analysis.
Created by V. Anderson 2013-2014