Properties of pennies
Guided inquiry lab experiment
Student handout
Introduction
In this experiment, students will devise a procedure to determine the average density of a
sample of pennies. Students will communicate results, hypothesize reasons to explain
discrepancies in experimental results, and using known densities of pure metals, calculate the
percent composition of pennies.
Materials
• 10 U.S. pennies
• Electronic balance
• Plastic weigh boats
• 100-mL graduated cylinder
• Metric ruler
Background
Throughout the penny’s history, its composition has changed as different metals have varied in
abundance and value.1 From 1793 to 1837, the penny was made out of pure copper. From
1837 to 1962, copper was alloyed with tin, zinc, or nickel, depending on the year. In 1943,
most pennies were composed of zinc-coated steel, as copper was in high demand for the
United States’ efforts in World War II. In 1962, tin was removed from the penny, leaving only
copper and zinc, which have been used to make the penny ever since.
For simplicity, only pennies minted after 1962 will be used in this experiment, limiting the
metals used to copper and zinc. Their densities and melting points are presented below.2
metal
copper
zinc
density (g/cm3)
8.92
7.14
melting point (0C)
1084.62
419.53
Given the supplied materials, develop a procedure to determine the density of the pennies in
your sample, and determine the composition of copper and zinc in the pennies in your sample.
Remember that you need to find the mass and volume of the pennies in order to calculate the
density.
Procedure
In your lab notebook, write a procedure to determine the average density of the pennies in your
sample using materials supplied. Have your instructor review your procedure before you begin
making measurements.
Developed by Jeremy S. Sandrik, Michigan Tech Department of Chemistry, 2010
1
Data & Observations
In your lab notebook, create a data table and record your numerical data. Remember to clearly
label your data and include units with all measurements. Also, save room for writing
descriptive qualitative observations.
Results & Conclusions
In your lab notebook, answer the following questions.
1. Calculate the average density of your sample of pennies. Remember to show your work
and use proper units.
2. Discuss any differences between your sample’s average density and those of your
classmates. Suggest possible hypotheses to explain any differences and propose tests for
your explanations.
3. Using your calculated density of the penny and the densities of pure copper and zinc,
calculate the average percent composition of copper and zinc in your sample of pennies.
Record your density and percent composition on the chalkboard for comparison with the
rest of the class.
4. If time permits, you or your instructor may perform tests of your hypotheses from #2.
Record your observations of those tests.
5. If you measured the mass of wet pennies, how would your calculated density be affected?
Would it be too high or too low?
6. If the year was scratched off of a penny, how could you use the measured density to
estimate the date it was made?
7. Describe another scenario in which determining the density of an object or substance would
be useful to identify it.
References
1. The United States Mint. Fun Facts about the United States Mint: The Composition of the
Cent. http://www.usmint.gov/about_the_mint/fun_facts/?action=fun_facts2 (accessed Jun
8, 2010).
2. Winter, M. The University of Sheffield and WebElements Ltd, UK.
http://www.webelements.com/ (accessed Jun 8, 2010).
3. Becker, R. “Pennies Old and New.” Twenty Demonstrations Guaranteed to Knock Your
Socks Off! Volume II.; Flinn Scientific: Batavia, IL, 1997.
Developed by Jeremy S. Sandrik, Michigan Tech Department of Chemistry, 2010
2