Name _________________________________ Date ________________ Period _______
Partner(s) ________________________________________________________________
DENSITY OF PENNIES LAB
Before 1982, pennies were made of a copper alloy. Since then, they have been made
with an outside coating of copper and an inner core of a different metal. In this
experiment, you will use a graph to determine the density of pre-1982 pennies. Then, you
will use known density values to identify the metal used in the core of the post-1982
pennies. You will also measure and use the densities of several other metals to
determine the identity of an unknown metal.
MATERIALS
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pre-1982 pennies
post-1982 pennies
metal cylinders
100-mL graduated cylinder
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electronic balance
graph paper
ruler
your brain 
Part 1-PROCEDURE
1. Zero (TARE) the balance with a plastic weighing tray on it.
2. Record the mass of 5 pre-1982 pennies in Data Table 1.
3. Fill the graduated cylinder with about 20 mL of water. Record the exact volume of water
under “Initial Volume” in the data table to the correct number of significant figures (measure
one place past what you can see on the graduated cylinder). This will be your initial
volume for the entire experiment.
4. Put the pennies in the graduated cylinder and record the Final Volume in mL.
5. Mass 5 more pre-1982 pennies. Add this mass to the mass of the original 5 pennies so you
now have the mass of 10 pennies. Record the total mass of 10 pennies in the data table.
6. Add the pennies to the graduated cylinder and record the new final volume.
7. Repeat steps 5-6 until you have a total of 30 pennies.
8. Find the total volume of copper for each set of data.
DATA TABLE 1 (Pre-1982 Pennies)
# of Pennies
Mass (g)
Initial Volume
(mL)
Final Volume
(mL)
5
10
15
20
25
30
*Record the appropriate number of significant figures for each measurement.
Volume of
Copper (cm3)
ANALYSIS
1. Graph the volume of pennies (x-axis) against the mass of pennies (y-axis) for the pre1982 penny data. Draw a best-fit line that goes through the point (0,0). Remember to follow
the Graphing Guidelines from your handout!
2. To calculate the density of the pennies, find the slope of the line using any two points on the
line (rise over run or (y2-y1)/(x2-x1)). Indicate on the graph which points you are using and
show your calculations. Round your answer to the correct number of significant figures and
use units for density in your answer.
3. Find the percent error of your calculated density. The accepted value for the density of
copper is 8.92 g/cm3.
Part 2-PROCEDURE
1. Follow the procedure in Part 1 with post-1982 pennies.
DATA TABLE 2 (Post-1982 Pennies)
# of Pennies
Mass (g)
Initial Volume
(mL)
Final Volume
(mL)
Volume of
Copper (cm3)
5
10
15
20
25
30
*Record the appropriate number of sig figs for each measurement.
ANALYSIS
1. Use a different colored pen or pencil to graph the volume of post-1982 pennies against
mass on the same graph you used for part 1. Draw a second best-fit line for the post-1982
penny data.
2. Find the slope of the new line to calculate the density of the post-1982 pennies. Indicate on
the graph which points you are using and show your calculations. Use the appropriate
number of significant figures and units in your answer.
Part 3-PROCEDURE
1) Zero the balance without the plastic weighing tray.
2) Find the mass of the zinc sample. Record it in Data Table 3.
3) Fill the graduated cylinder with about 20 mL of water. Record the exact volume of water
under “Initial Volume” in the data table to the correct number of significant figures.
4) Put the zinc in the graduated cylinder and record the Final Volume.
5) Repeat steps 2-4 for, aluminum, iron, and your unknown sample.
6) Use the data from Part 1 to get the information for copper.
7) Predict the identity of your unknown metal using qualitative observations and the
quantitative calculated densities for the known metals.
DATA TABLE 3 (Identifying and Unknown)
Element
Mass (g)
Initial Volume
(mL)
Zinc
Aluminum
Iron
Copper
Unknown
ANALYSIS
1. What is the identity of the unknown metal?
2. How do you know?
Final Volume
(mL)
Density (g/mL)
CONCLUSIONS
Answer the following questions as thoroughly as possible in complete sentences. In your
discussion of precision and accuracy, make it clear that you understand the difference between
these two terms.

Examine both graphs and discuss the precision of your measurements. Clearly explain how
your graphs demonstrate precision.
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Use your calculated percent error to discuss the degree of accuracy in this experiment.
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Based on your calculated density in Part 2 and the table below, which metal do you think is
used in the core of post-1982 pennies? Explain your choice. State both values for
comparison.
Metal
Density (g/cm3)
magnesium
aluminum
zinc
copper
silver
lead
1.74
2.70
7.00
8.92
10.50
11.35
BONUS
You could find the thickness of a piece of aluminum foil without actually measuring it. How
would you go about this? Explain in detail using formulas and example calculations.