Isotopes of Pennies Pre Lab
You will do a lab that will deal with isotopes, mass number, and atomic mass. Before you begin your work in
the lab, try to explain these terms in your own words. After you have finished the lab, you will have a chance
to revise your explanations based on what you have learned in the activity.
Isotope:
Mass number:
Atomic mass:
In 1982, the United States government changed the way it minted pennies. Before 1982, pennies were made
of 95% copper and 5% tin. Now they are made of zinc coated with copper. Because they weigh different
amounts (have different masses), we can call them isotopes of pennies.
1. What do the two kinds of pennies represent in this exercise?
2. How do the pennies differ? How do isotopes differ?
3. What do the pennies have in common? What do isotopes have in common?
Isotopes of Pennies Lab Lab
Part A (note: answers should only be as accurate as your instrument.
Remember, “significant digits!!!”)
1. Obtain a sample of 13 pennies (clear container).
2. Mass several pre-1982 (old) pennies and record their average mass.
______g
show work here:
3. Mass several post-1982 (new) pennies and record their average mass.
______g
show work here:
4. Calculate the mass of 3 old pennies plus 7 new pennies.
______g
show work here:
5. Find the average mass for the last answer.
______g
show work here:
6. Now mass a sample of 3 old and 7 new pennies. Record the mass.
______g
7. Find the actual average mass of a penny in your sample.
______g
show work here:
9. Compare your answers for numbers 4&6 and 5&7… Are they the same? If not – Why?!
8. Compare your answer for number 5 to your answer for number 7. Is your average mass closer to the mass
of an old penny or a new penny? Why?
9. How is this average mass related to atomic mass?
Part B
1. Now let’s use 6 old pennies and 4 new pennies…
2. Using the mass of an old penny and a new penny from Part A above, calculate the average mass for this
sample of pennies.
show work here:
______g
3. Now mass your sample of pennies. Record the mass.
______g
4. Find the actual average mass of a penny in this sample.
______g
show work here:
5. Compare your answer from number 2 to your answer for number 4. Is the average mass closer to the mass
of an old penny or a new penny? Why does this happen? Is it a similar reason as in part A?
Part C: The Mystery Sample
1. Return your sample of 13 pennies and get a canister of pennies. Don’t open it.
Write its identifying letter here:______
2. Record the mass of the empty film canister, which is on the canister.
______g
3. Mass the sealed film canister containing ten mixed pennies.
______g
4. Return the canister.
5. Do some math… Fill in the chart on the next page. Using it, you can determine the contents of your mystery
sample!! Check with me and I’ll tell you if you were correct!!
Calculations:
# of New
Pennies
0
# of Old Pennies
Total Mass (g)
10
1
9
2
8
3
7
4
6
5
5
6
4
7
3
8
2
9
1
10
0
1. How many old pennies did your container have? ______
2. How many new pennies did your container have? ______
3. What percentage of old and new pennies do you have?
Average Penny
Mass (g)
Calculations:
Guess what?! You can use Algebra (you can thank me later…) to find out the number of new and old pennies
in your mystery sample. Create a verbal model using the following terms:
total mass
old penny mass
new penny mass
# of old pennies
# of new pennies
Verbal Model:
knowns (# values)
unknowns (algebraic expression (1 variable))
old penny mass =
# of old pennies:
new penny mass =
total mass =
# of new pennies:
Write the algebraic equation, solve it and answer the questions below…
1. How many old pennies did your container have? ______
2. How many new pennies did your container have? ______
3. What percentage of old and new pennies do you have?