PENNY ISOTOPES
You will need some paper and a calculator for
this lab.
1. Mass of pennies

Record the number of pennies in your
container. List them by year – then record the
mass of each penny next to the year it was
manufactured. Use the electronic balances
and be sure to record ALL digits on the display.
Some years may be duplicated – record each
penny individually.
2. Pennies an analogy for Isotopes




Pennies manufactured prior to 1982 were 95%
copper, 5% zinc.
Pennies manufactured after 1982 are 5%
copper, 95% zinc.
Pennies manufactured in 1982 are a mix of the
older and newer types.
So pennies seem to have 2 ‘isotopes.’
3. Averages

Calculate the average mass of the pennies in
your sample which were made before 1982.

Calculate the average mass of the pennies in
your sample which were made after 1982.
4. Average Atomic Mass
Use the formula:
Average Atomic Mass = (% of 1st Isotope X Mass
of 1st Isotope) + (% of 2nd Isotope X Mass of
2nd Isotope)

Calculate:
% of pre-1982 pennies in your sample.
% of post-1982 pennies in your sample.
4. Average Atomic Mass

Use the average masses you calculated in
Step 3 and the % of each isotope to calculate
the ‘Average Atomic Mass’ of a penny.
(Remember to either change % to a decimal –
50% is .5, OR divide your final answer by 100.
I prefer to change % to a decimal at the
beginning, since it leaves one less thing to
forget.)
5. Density

Based on the average masses for pre- and
post-1982 pennies and the composition
information given in slide 2, which metal must
be more dense – Copper or Zinc?

Use your textbook, the internet, or some other
source to verify your answer. Record the
actual densities of copper and zinc here.