The
Composition of Pennies Lab pgs. 38-39
Background Information: U.S. pennies have been composed of
copper and zinc since 1959, but the ratio of copper to zinc has changed over
the years because of increases in the price of copper. Copper and zinc are both metallic
elements and share many physical properties, but they have different
densities. Pure copper has a
density of 9.0 g/mL, while pure zinc has a density of 7.1 g/mL. By measuring the densities of penn=
ies
from different years, it’s possible to track changes in the compositi=
on
of the penny.
![](3D"The_Composition_of_Pennies_Lab_files/image002.jpg")
PROBLEM: (can be ch=
anged
to form hypothesis)
What
are the approximate composition of pennies having various mint dates?
HYPOTHESIS:
O=
BJECTIVES:
Measure mass and
volume and determine the density of pennies.
Interpret class=
data
to determine approximately when the composition of pennies changed.
M=
ATERIALS:
5 pennies of va=
rying
mint dates
Balance sensiti=
ve to
0.01g
50-mL graduated
cylinder having 1-mL graduations
S=
AFETY
PRECAUTIONS
![](3D"The_Composition_of_Pennies_Lab_files/image004.gif")
Wear goggles an=
d laboratory
aprons.
P=
ROCEDURE
1. Record the m=
int
date of each penny in the data table.
2. Mass each penny and record the mass to the neare=
st
0.01 g.
3. Run tap wate=
r into
the graduated cylinder until it is approximately one-half full. Read and record the volume to the
nearest 0.1 mL.
4. Carefully ad=
d the
five pennies to the cylinder so that no water splashes out. Jiggle the cylinder to dislodge any
trapped air bubbles. Read and
record the total volume of the water and the five pennies.
D=
ATA
AND OBSERVATIONS
|
VOLUME
of Water (mL) |
|
|
VOLUME
of Water + 5 Pennies (mL) |
|
|
VOLUME
of 5 Pennies (mL) |
|
|
Average
volume of a penny (mL) |
|
|
MINT DATE |
Mass (g) |
Volume (mL) |
Density (g/mL=
) |
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ANALYZE AND CON=
CLUDE
1. Calculating<=
span
style=3D'mso-spacerun:yes'> Subtract the
initial volume of water plus pennies to calculate the volume by 5 to calcul=
ate
the average volume of a penny.
Record this volume in the data table. SEE DATA=
TABLE
2. Calculating Calculate the
density of each penny by dividing its mass by the average volume. Post your results so they are avai=
lable
to the other members of your class.
SEE DATA TABLE
3. Observing and Inferring Does your group
data show any pattern that relates the densities of the pennies to the mint
date? =
Describe the pattern:
4. Classifying<=
span
style=3D'mso-spacerun:yes'> Classify=
the
pennies of each year that your group examined as mostly copper (8.96 g/mL) =
or
mostly zinc (7.13 g/mL).
APPLY AND ASSES=
S
1. <=
span
style=3D'font-size:16.0pt;font-family:"Arial","sans-serif";mso-bidi-font-we=
ight:
bold'>What factors do you think might lead to error in your density
measurements?
Which of these factors could not be corrected by improved technique?<= o:p>
2. <=
span
style=3D'font-size:16.0pt;font-family:"Arial","sans-serif";mso-bidi-font-we=
ight:
bold'>Explain how you might determine the identity of an irregularly shaped
solid that is soluble in water.
3. <=
span
style=3D'font-size:16.0pt;font-family:"Arial","sans-serif";mso-bidi-font-we=
ight:
bold'>In 1943, all pennies issued by the U.S. mint were struck from zinc-pl=
ated
steel. Two of these pennies a=
re
shown in the photo. Why were steel pennies struck in 1943?
What was the purpose of the zinc coating?
4. <=
span
style=3D'font-size:16.0pt;font-family:"Arial","sans-serif";mso-bidi-font-we=
ight:
bold'>Why would increases in the price of copper cause the mint to change t=
he
composition of pennies?
![](3D"The_Composition_of_Pennies_Lab_files/image006.jpg")