As you learned from the “Hollow Penny” activity, pennies minted before 1982 are pure copper. Newer pennies are actually almost entirely composed of zinc, but the thin coating of copper on the outside makes new pennies look very much like they are made of copper. Copper and zinc are different elements and therefore have different density
values. By determining the density
of each type of pennies, the composition of the metal can be confirmed. Older copper pennies should have a different ratio
(density) than zinc pennies.
Use the internet to find the theoretical density
of zinc and copper. Look for units of grams/cm3
. Use this information to make a hypothesis
for the experiment.
of copper = ____________g/cm3
of zinc = ____________ g/cm3
- Using the mint dates, separate out the pennies into a copper and a zinc pile. You will need 15 pennies of each type.
- 2. Place 50.0 mL of water into a graduated cylinder. Record the initial water level of water as 50.0 mL.
- 3. Put the cylinder on the balance. Record the initial mass of the cylinder and water.
- Add 3 copper pennies to the cylinder. Notice that the water level rises. Record the final water level. The volume of the pennies can be determined by water displacement (i.e. by taking the difference between the volumes).
- Put the cylinder on the balance. Record the mass of the cylinder, water and the pennies.
Find the mass of the coins by subtraction.
- Add three more pennies, so that there is a total of 6 coins in the cylinder. Record the volume and the mass.
- Keep adding the pennies, in groups of 3, until you have put all 15 copper pennies into the water.
- When finished with the copper pennies, repeat the process using zinc pennies.
Data for the copper pennies
Data for the zinc pennies
Calculate the density for each trial.
Since you have five density
values, find the average density
for each metal.
Compare the theoretical density
to the average experimental density
by calculating the % error.
Using your graphing calculator or LoggerPro, create a graph
(y-axis) versus volume
(x-axis) for each metal. You will plot the five data
points for each metal. Calculate the slope
of each line. The slope
represents the mass/volume or the density
of the metal. Both lines can be plotted on the same graph
so that the results can be easily compared.
Print out a copy of the graph
to include in your lab report. Be sure to write the slope
of each line
on the graph.
- State your results. What is the average experimental density for each metal?
- State the theoretical value.
- State the % error.
- Think about and suggest at least two valid sources of error.
Suggest at least two ways to improve the experiment.