Isotopic Penny Lab
Pre-1982 and post-1982 pennies have different compositions. The change in
composition occurred because of the rising cost of copper in the early eighties. The
federal government decided to mint pennies with zinc on the interior because zinc was
less expensive to obtain. The incorporation of zinc in the pennies causes pre-1982
pennies to have a different mass than post-1982 pennies, and consequently a
different overall density.
In this laboratory activity, a mixture of these pennies will represent the naturally
occurring mixture of two isotopes of the imaginary element “coinium.” With the pennies,
you will simulate one way that scientists can determine the relative amounts of different
isotopes present in a sample of an element. Isotopes are atoms with the same number
of protons but different number of neutrons. For example, carbon-12 and carbon-14 are
two isotopes with 6 protons each, but C-12 has 6 neutrons and C-14 has 8 neutrons.
These two isotopes have different masses because they have a different number of
neutrons. The atomic mass of an element given on the periodic table is the average
mass based on the relative abundance of its isotopes.
You will be given a sealed film canister containing a mixture of pre-1982 and post-1982
pennies. Your container could contain any combination of the two “isotopes.” Your task
is to determine the isotopic composition (number of pre-1982 and number of post-1982)
of the element “coinium” without opening the sealed canister.
Procedure
1. Obtain 5 pre-1982 pennies and 5 post-1982 pennies, a sealed film canister of 10
mixed pre- and post-1982 pennies, and an empty film canister.
2. Record the code letter on the sealed film canister. Do NOT open the sealed film
canister!
3. Find the mass of a single pre-1982 and single post-1982 penny by massing a stack of
5 pennies from each age range and taking the average. Record the data in your data
table.
4. Find the mass of the sealed film canister of pennies. Find the mass of the empty film
canister. Record both of these numbers in your data table.
5. Calculate the total mass of the mixture of pennies. Record the data in your data table.
Pre-lab Questions
1. What is an isotope?
2. How are isotopes of the same element similar?
3. How are isotopes of the same element different?
4. Why is it necessary to record the mass of the empty film canister?
Data Table
Code letter/number on sealed film container
Mass of single pre-1982 penny
Mass of single post-1982 penny
Mass of sealed film container with mixture of
pennies
Mass of empty film container
Total mass of mixture of pennies
Number of pre-1982 pennies in your mixture
Number of post-1982 pennies in your mixture
Data Analysis
1. Calculate the number of pre-1982 pennies and post-1982 pennies in your mixture by
using and solving a system of equations (Refer to D 3-1 if needed). Record the number
of pre-1982 pennies and post-1982 pennies in your data table. Show your work clearly.
2. a. What intensive physical property of the element “coinium” distinguishes its pre1982 and post-1982 forms from each other? (Refer to Units 1 & 2)
b. What extensive physical property of the element “coinium” distinguishes its pre-1982
and post-1982 forms from each other?
3. Why is the element “coinium” a good analogy or model for actual element isotopes?
4. In what ways is the analogy misleading or incorrect? How is “coinium” not like an
actual isotope?
5. Name one other familiar item that could serve as a model for isotopes. Explain why it
would be a good model for isotopes (You must completely explain how it is like an
isotope to receive credit).