Chemistry Activity
Name: ______________________________
Penny Abundance: Counting by Weighing
Block: ______ Date: __________________
Your task is to determine the total number of pennies in the jar without opening the jar!
Materials
 an assortment of pennies, including some pre- and some post-1982
 a centigram balance
 a kilogram balance
Useful Information
 mass of the jar and top (without pennies): 242.2 g

percentage of pre 1982 pennies in the jar: 30.1

percentage of post 1982 pennies in the jar: 69.9
Good luck!
Hand draw a data table for recording any measurements in the space below.
Show your work for the calculation of the number of pennies in the jar below.
calculated number of pennies in the jar: _____________________
uncertainty: (plus or minus) _____________________
Chemistry Activity
Name: ______________________________
Penny Abundance: Counting by Weighing
Block: ______ Date: __________________
Post-Activity Questions
1. What is the average mass of a penny in the jar?
2. Do any of the pennies in the jar actually have the same mass as the average mass? Explain.
3. How many pennies are in 2.00 tons of pennies, assuming the same composition as the
pennies in the jar? What is the uncertainty?
(1 ton is defined as exactly 2000 lbs.; 1 lb measures as 453.5 g)
# of pennies
_______________
uncertainty
_______________
4. The element boron consists of two isotopes, boron-10 and boron-11.
a. How are boron-10 and boron-11 alike?
b. In what two ways are boron-10 and boron-11 different?
1.
2.
c. How are pre 1982 and post 1982 pennies like boron isotopes?
5. A single boron-10 atom has a mass of 10.01 amu, or atomic mass units. An atomic mass unit
is an extremely small mass, about the mass of a proton or neutron, used for atoms. It will be
defined later in the module. A single boron-11 atom has a mass of 11.01 amu. 19.9 percent
of naturally occurring boron is B-10, and 80.1% of naturally occurring boron is B-11. What
is the average mass, in amu, of a boron atom in nature?
6. Do any boron atoms have the same mass as the average mass of a boron atom in nature (your
answer to #4)? Explain.
7. Look at boron on the periodic table. Does anything strike you (hint-the answer is yes). What
strikes you?
8. Do you think a random sample of pennies taken from various locations in the United States
would have the same composition of pennies (30.11% pre-82, and 69.89% post-82) as the
pennies in the jar? Explain.
9. Do you think a random sample of carbon taken from various locations on Earth would have
the same isotopic composition (percentages of the different isotopes of carbon)?