Student:________________________________
Lab Partner:_____________________________
Date:__________________________________
General Chemistry Lab 1025C
Comparing the Density of Pennies-SL
Introduction: Occasionally the US Department of Treasury changes the composition of pennies, which changes the
overall mass and density of each coin. In this experiment, you will determine the average density of two groups of
pennies made at different times. Then you will compare the average densities of the pennies in the two groups.
Objectives: Determine the average densities of pennies by using mass and volume. Compare the average densities of
pennies made before 1982 and after 1982. Infer the change made in the composition of pennies in 1982.
Materials:
Triple Beam Balance
Pennies Coined After 1982
Pennies Coined Prior to 1982
100 ml Graduated Cylinder
Water
Plastic Cups
Paper Towels
Procedure:
1. Sort your pennies into two piles. One pile should contain 10 pennies coined prior to 1982, and one pile should
contain 10 pennies coined after 1982. You do not want any pennies coined in 1982.
2. Use the balance to measure mass of the plastic cup without the Pre-1982 pennies. Record this mass in grams
(0.001 g) in your data table. Then use the balance to determine the combined mass of the pennies in the pre1982 group and the plastic cup. Record this mass in grams (0.001 g) in your data table. Then use the balance
to measure mass of the plastic cup without the Post-1982 pennies. Use the balance to measure the combined
mass of the pennies in the post-1982 group and the post-1982 pennies. Record this mass in grams (0.001 g) in
your data table. For each group, determine the combined mass of the pennies without the cup and record this
data in your table.
3. Fill a graduated cylinder about half way with water. Read the volume of the water correctly by reading the level
according to the meniscus. Remember you should always put your eye at the level of the bottom of the
meniscus.
4. Record the volume of the water in milliliters to 0.1 ml.
5. Now very carefully to avoid breakage of the graduated cylinder and spillage of water, add the group of pre-1982
pennies to the water in the graduated cylinder. Measure the new volume of the water and the pennies
combined. Record this volume.
6. Carefully remove the pennies by pouring the water into the sink using your hand to catch the pennies. Dry the
pennies on a paper towel.
7. Repeat the procedure for the post-1982 pennies.
8. When you are finished, rinse the graduated cylinder with tap water twice, and then distilled water twice. Then
return the cylinder to the instructor. Dry your pennies and return to your instructor in their appropriate cups.
9. Now it is time to do your calculations and analysis and research. Remember to use separate paper and label your
sections.
Analysis:
1. What is the density of copper? ____________________________________
2. What is the density of zinc? _________________________________________
3. According to your calculations, which group of pennies has the greater average density, pre-1982 or post1982? ______________________________________________
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4. Based on the density of copper and zinc and your answer in question 3, do you think the ratio of copper to
zinc in the pennies made after 1982 is higher or lower than the ratio of copper to zinc in the pennies made before
1982? Why? Be clear and specific, and use complete sentences.
5. Compare your experimental densities for the pre and post 1982 pennies to the actual densities for pennies pre
and post 1982. To determine the actual densities of pre and post 1982 pennies, use your density values for
copper and zinc and plug them into the formula below where x and y represent the % composition of copper and
zinc.
(x)(7.13 g/mL) + (y)(8.96 g/mL) = density (g/ml)
You will find the following website helpful:
http://www.usmint.gov/about_the_mint/fun_facts/index.cfm?action=fun_facts2
To calculate percent, use the equation below:
%Error = Actual Density – Experimental Density
Actual Density
x 100%
After determining your % error, suggest possible sources for error.
Research:
Research changes in the composition of pennies made by the US Department of the Treasury in the past century. Write a
minimum of 2 paragraphs describing the changes and explaining why you think the changes were made. You must cite
your sources (MLA). You must write this portion on a separate sheet of paper and in complete, grammatically
sentences. Remember to write your findings in your own words. Do not plagiarize.
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Table of Data Penny Lab
Group
# Coins
Mass of
Empty
Cup
Mass of
Cup and
Pennies
Mass of
Pennies
(g)
Volume of
Water
(ml)
Volume of
Water and
Coins
(ml)
Volume of
Coins
(ml)
Density of
Coins
(g/ml)
Pre-1982
Pennies
Post-1982
Pennies
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