Density Pennies

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					Lab 5 - Measuring Densities of Pennies
Archimedes, a Greek mathematician of the second century BC, was commissioned by the
king of Syracuse to find whether a crown that had been made for the king was fashioned
from pure gold or from a mixture of gold and silver. Archimedes could not use chemical
tests or damage the crown in any way, yet he was able to answer the king’s question.
How did he carry out the king’s request? In this experiment, you will use methods
similar to Archimedes’ to study differences in pennies.

Today’s penny is not the same as the penny of yesteryear. Before 1982, pennies were
made mostly of copper. In this experiment, you will determine and compare the densities
of pennies minted before 1982 and after 1983, and use density data to try to identify the
metal used in the core of pennies minted after 1983.

Procedure
1. Work with one set of pennies at a time, either pre-1982 or post-1983 pennies. Find
   the mass of 5 pennies from one set. Record the mass.
2. Add 5 more pennies to the first group and obtain the mass of these 10 pennies.
   Record the mass.
3. Repeat step 2, each time adding 5 more pennies to those already on the balance, until
   you have used all 25 pennies.
4. Fill a 50-mL graduated cylinder to the 20-mL mark with water. Be sure to use the
   bottom of the meniscus to determine the water level.
5. Still working with the same set of pennies, gently drop 5 of the pennies into the
   graduated cylinder. Record the new water level in your data table.
6. Add 5 more pennies to the cylinder, making a total of 10 pennies. Record the water
   level.
7. Repeat step 6, each time adding 5 more pennies to the cylinder, until you have used
   all 25 pennies. Record the volume after each addition.
8. Discard the water. Thoroughly dry the pennies with a paper towel and return them to
   the appropriate baggie.
9. Repeat steps 1-8 using the 25 pennies in the other set of coins. Record all data.

Questions
1. Calculate the net volume (the volume of the pennies only) for each group of pennies.
2. Construct a graph of results. Let the y-axis reflect the mass of the pennies and the x-
   axis be the volume. Plot the data for the pre-1982 pennies and draw a best-fit line.
   Plot the post-1983 data on the same graph and draw the best-fit line. Clearly label
   each line.
3. Compare and contrast the graphs – how are they similar? How are they different?
4. Find the slope of each line.
5. What is the significance of the slope? What do the values represent?
6. How does the density of the pre-1982 pennies compare with the actual density of
   copper?
7. Using your results, hypothesize what metal(s) might be inside the inside the post-
   1983 penny.
                  PRE-1982                      POST-1982
                  PENNIES                        PENNIES
Number     Mass   Initial   Final     Net    Mass   Initial   Final     Net
of Coins    (g)    mL        mL     Volume    (g)    mL        mL     Volume
                                     (mL)                              (mL)
   5



  10



  15



  20


  25

				
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