Chemistry –CP and Honors Lab #1 Student Name: __________________ Date(s) Lab was completed:___________ Level:______
Partner(s) Name___________________
Lab: A Penny For Your Thoughts
Background: (This is an example of a well written Background so you have for future labs reports)
Density is defined as the ratio of mass to volume, and its formula is density = mass ÷ volume. The units for
mass are grams (g). The units for volume are either cubic centimeters (cm3) or milliliters (mL), so the units for
density can either be g/cm3 or g/mL.1
Density is a physical property that can be used to identify an unknown substance. It is also considered an
intensive property; that is, the density of an object does not depend on how much of the substance is present.
For example the density of water is 1.00 g/ml. Whether you have a drop, a glass, or a bucket of water, its
density is always 1.00 g/ml.
Over 2000 years ago King Hieron of Syracuse suspected that the jeweler who made his gold crown had mixed
the gold with another cheaper metal. Although the king could measure the mass of the crown, its intricate
design prevented measurement of its volume.2
King Hieron hired Archimedes, a Greek mathematician, physicist, and engineer to solve his dilemma.
Archimedes knew that in order to solve the problem, he had to calculate the density of the crown and match it to
the density of pure gold.
While taking a bath, Archimedes noticed the water level rise as he lowered himself into the tub and knew he
had the solution. He could find the volume of the crown by measuring how much water it moved, or displaced.
(This method is now known as water displacement). He was so excited about his great discovery that he ran
through the streets of Syracuse naked shouting "Eureka!" which is Greek for "I have found it."
Using the mass and volume of the crown, he calculated the density of the crown. The crown was indeed a fake.
Archimedes was a hero!3
Today’s penny is quite different from the penny of two decades ago. Before 1982, pennies were made of an
alloy (solid mixture with at least one component being a metal) of copper. Since then, they have been made
with an outside coating of copper and an inner core of a different metal. These differences in composition of
older and more recently minted pennies have resulted in differences in the pennies properties. One of these
differences is the density.
Purpose: In this lab, you will measure the mass and volume of two sets of pennies: pre-1982 pennies and
1982 and later pennies. You will then graph the data, calculate the slope of the lines, and determine the density
of the pennies. In this experiment you will make a study of some of the physical properties of U.S. pennies.
Remember: Color, shape, volume, mass, density, and hardness are examples of physical properties. We often
identify objects by their physical properties. Chemists also use physical properties to identify chemicals. (I am
providing this to you for direction and understanding in our 1st lab. Normally, you will have a Hypothesis
only.)
1 http://www.elmhurst.edu/~chm/vchembook/120Adensity.html 2 http://physics.about.com/od/fluidmechanics/f/density.htm 3 http://www.propertiesofmatter.si.edu/archimedes.html 1 Chemistry –CP and Honors Lab #1 Materials:
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Balance
(25) pre-1982 pennies and (25) 1982 and older pennies
50 mL plastic graduated cylinder
tap water
Hypothesis:
(You are to develop this, based on your understanding of density and pre/post 1982 pennies)
Procedure:
1) Mass five pre-1982 pennies. Record this value to the hundredths place in your data table.
2) Determine the volume of the five pennies by water displacement.
things to keep in mind when measuring the volume of the pennies: ü read the graduated cylinder to the tenths placeread the graduated cylinder at eye-level
ü slide the pennies into the graduated cylinder gently; avoid splashing any water onto the sides of the
graduated cylinder
ü tap the graduated cylinder on the lab table to eliminate any air bubbles have formed between pennies
ü keep the pennies in the graduated cylinder until you finish collecting data for all 25 pennies
3) Repeat steps 1 and 2 until you have collected data for at least 25 pennies.
4) Repeat steps 1 – 3 for 1982 and older pennies.
Data: Copy the provided data tables (twice!) into your lab notebook before coming to class. Use a
ruler/straight edge and make sure to make a data table for each penny.
Penny Category: Pre-1982 or Post-1982?
Trail Number
Mass
g
Initial Volume of
Water
mL
Final Volume of
Water
mL
Volume of
Pennies
mL
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2
3
4
5
2 Chemistry –CP and Honors Number of Pennies
Lab #1 Mass
g
Vol. of pennies
mL
5
10
15
20
25
Graph:
1. Make a graph of mass vs. volume for each data set. Mass should be on the y-axis, and volume should be on
the x-axis. You will plot two lines on this single graph (one line for each data set).
2. Plot points for each set of data (use a different color for each data set and include a legend on the graph).
Draw a small circle around each data point.
3. Draw best-fit lines for each data set on your graph (again, use different colors).
4. Find 2 "nice" new points on each best fit line, and make a square around them in yet another color.
5. Label the “nice” points (x1, y1) and (x2, y2) for each line.
Calculations:
1. Calculate the slope of each best-fit line. Include units and significant figures in your answer. Remember the
equation of slope is:
Slope = (y2 -y1)
(x2 - x1)
2. According to the US Mint (www.usmint.gov), pennies minted before 1982 are made of copper (density =
8.96 g/ml). Compare your experimental density value with the accepted value by calculating your percent error
for the density of a pre-1982 penny:
Percent Error = (Experimental Value – Accepted Value) X 100%
Accepted Value
3. Since 1982, pennies have been comprised of an inexpensive “unknown” metal surrounded by copper plating.
The US Mint states that new pennies still contain about 2.5% copper in the plating. Using your experimental
density value for post-1982 pennies, and the information provided by the mint, calculate the density of the
unknown metal.
3 Chemistry –CP and Honors Lab #1 4. Determine the identity of the unknown metal using the chart below. Include an explanation of your logic.
Metal
Density (g/cm3)
Gold
19.32
Iron
7.86
Lead
11.34
Zinc
7.13
Mercury
13.55
Tin
7.3
Titanium
4.5
Silver
10.5
Platinum
21.45
Nickel
8.9
Conclusion Questions: (You may need to write a complete conclusion without the help of questions in the future)
1. Explain what the slope of the line on a mass vs. volume graph represents in one sentence. What does the
graph you created tell someone who is reading this report about the samples of pennies you collected
data on?
2. Based on your previous experiences, list the following substances in order from the lowest density to the
highest. Explain your reasoning; provide evidence for your explanation using examples to support your
conclusions. (Lead pipe, water, pine 2” X 4” board, Styrofoam, peanuts).
3. Identify one area of engineering (applied research) where the density of a material might be important.
Be specific and explain your answer.
Science GSE’s
PS1 a- measuring mass and volume of both regular and irregular objects and using those values as well as
relationship d=m/v to calculate density.
PS1 - 2a Students demonstrate and understanding of the characteristic properties of matter by identifying
unknown substances
JHS Student Expectations
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Reads actively and critically for a variety of purposes. Writes and speaks effectively. Listens and views materials actively and critically. Reasons effectively and solves problems.
Performs and applies numeracy skills for a variety of purposes
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