Name ___________________________________
ISOTOPES OF PENNIUM LAB (BIOLOGY)
Period _______ Date ____________ Seat ______
Introduction
Unless you’re a coin collector, you probably think all United States pennies are pretty much the same. To the casual observer, all the
pennies in circulation do seem to be identical in size, thickness, and composition. But just as elements have one or more isotopes
with different masses, the pennies in circulation have different masses. In this investigation, you are going to mass pennies of
different dates to determine if there are any “isotopes” of an imaginary element called pennium, or Pe. Remember that chemical
isotopes are atoms that have the same number of protons, but different numbers of neutrons. Thus, chemical isotopes have nearly
identical chemical properties, but some different physical properties. In this investigation, you will determine the relative abundance
of the isotopes of pennium and the masses of each isotope. You will then use this information to determine the atomic mass of
pennium. Recall that the atomic mass of an element is the weighted average of the masses of the isotopes of the element. This
average is based on both the mass and the relative abundance of each isotope as it occurs in nature.
Problem
What are the masses and the relative abundances of pennium and what is the atomic mass of the element?
Materials
Laboratory balance
20 pennies
Procedure
1. Count out 20 pennies from the penny container from the years 1965 to 2010. No two pennies should have the same year. If
so, switch them out so that you have 20 pennies, each with a different date.
2. Find the mass of all 20 pennies. Enter this as the total mass of 20 pennium atoms in question 1 on page 3.
3. Find the mass of each penny separately. In the Data Table, record the penny’s mass to the nearest 0.1 g and the year minted.
4. Place the 20 pennies back in the container. Clean up your work area and wash your hands.
5. Plot the mass of each penny as a function of its date on the graph provided on page 2.
6. Answer the questions on page 3.
Penny No.
Penny
Year Minted
Penny Mass
(0.1g)
1
2
3
4
5
6
7
8
9
1
10
11
12
13
14
15
16
17
18
19
20
Name ___________________________________
ISOTOPES OF PENNIUM LAB (BIOLOGY)
Period _______ Date ____________ Seat ______
Count out 20 pennies from the penny bucket. Record the mass of each penny as a function of its date.
3.4
3.3
3.2
Penny Mass (g)
3.1
3.0
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2010
2005
2000
2
1995
1990
1985
1980
1975
1970
1965
Penny Date
Name ___________________________________
ISOTOPES OF PENNIUM LAB (BIOLOGY)
Period _______ Date ____________ Seat ______
Questions:
5. Compare the average atomic mass of your sample with the average atomic
1. What is the total mass of your 20 pennium atoms = _________ g
mass of three other student groups. Are the average atomic masses for
2. Find the average atomic mass of the pennium (Pe) element using
following equation: Show how you set up the problem.
Average atomic mass =
each group the same? ___________
Explain why or why not.
Total mass of 20 pennieum atoms
__________________________________________________________
20 pennium atoms
__________________________________________________________
__________________________________________________________
6. What does each penny in this investigation represent?
_________________________________________________________
_________________________________________________________
7. What do the two different masses of the pennies represent?
You should notice the pennies fall into two groups, heavy and light.
_________________________________________________________
3. Count and record the number of each kind of penny: heavy and light.
_________________________________________________________
(isotope A) # of heavy pennies = _____
8. In what year(s) did the mass of Pe change? _____________________
_________________________________________________________
(isotope B) # of light pennies = _____
9. How can you explain the fact that there are different “isotopes” of
pennium? ________________________________________________
4. Calculate the percentage of occurrence of each isotope using the
following equations: Show how you set up the problems.
_________________________________________________________
_________________________________________________________
# of heavy pennies
%A=
total # of pennies
X 100
10. In addition to the two isotopes of pennium, there is a third that was
minted in 1943. Research the 1943 pennium isotope and discuss what
%B=
# of light pennies
total # of pennies
makes its mass different. ___________________________________
X 100
_________________________________________________________
3
_________________________________________________________