Pennium 1
Name ______________________________________________ Date _________ Period ______
Isotopes of Pennium
Purpose
After reading the lab, create your own purpose below:
______________________________________________________________________________
______________________________________________________________________________
Pre-Lab Discussion
In 1982, the United States government changed the way it minted pennies. Before 1982,
pennies were made of 95% copper and 5% tin. Since 1982, they have been made of zinc coated
with copper. Because each type of penny weighs a different amount, we can call them isotopes of
pennies. During this lab you will carefully measure and record data which will enable you to
perform calculations to determine the atomic mass of the fictitious element, Pennium.
Materials
Pennies
Balance
Calculator
Procedure
1. Obtain pennies from your teacher. Separate them by date into two groups: pre-1982 and
post-1982. Discard any pennies from 1982. The two groups are now the two isotopes of
Pennium.
2. In Table 1, count and record the number of atoms in each isotope and the total number of
atoms in your sample of Pennium.
3. Use the balance to determine the mass of each of 10 pennies from each group. Record in
Table 2.
Data
Table 1 – Atomic Mass Data
Pre-1982
Post-1982
Pennium
Total # of Atoms
Total Mass of
Atoms (g)
Average Mass of
1 Atom (g)
Relative
Abundance (%)
Relative Mass (g)
Atomic Mass of
Pennium (g)
100%
Pennium 2
Table 2 – Penny Masses
Pre-1982 Pennies
Penny #
Mass (g)
Post-1982 Pennies
Penny #
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
Mass (g)
Class average for the atomic mass of Pennium: ______________________
Calculations (Don’t write instructions, but include a sample calculation for each step)
1. Record the total mass of the 10 atoms in Table 2 as Total Mass of Atoms in Table 1.
2. Determine the average mass of one atom for each isotope by dividing the “Total Mass of
Atoms” by 10. Enter as Average Mass of 1 Atom in Table 1.
3. Determine the relative abundance of each isotope by dividing the “Total # of Atoms” for
each isotope by the “Total # of Atoms” in Pennium (Row 1, Table 1). Multiply by 100
and enter as Relative Abundance in Table 1.
4. Determine the relative mass of each isotope by multiplying the relative abundance for
each isotope by the “Average Mass of 1 Atom” for each isotope. Don’t forget to convert
the abundance percentage to a decimal. Record as Relative Mass in Table 1.
5. Determine the atomic mass of Pennium by adding the relative masses for both isotopes.
Record as Average Atomic Mass of Pennium in Table 1.
Questions
1. If the amount of post-1982 pennies was increased in your sample, what would happen to
the atomic mass? Explain.
2. In your own words, what is a weighted average? Give two examples, outside of
chemistry, where weighted average could/should be used.
3. How are the following isotopes alike and how are they different: 1H, 2H, 3H?
4. Copper has two isotopes, Copper–63 and Copper–65. The relative abundance of 63Cu is
72.70%. What is the atomic mass of copper?
Conclusion
What was your atomic mass for Pennium? How does it compare to the class average?
Explain (2+ reasons) why there could be different values for the average atomic mass of
Pennium in the class.