Name(s) ______

Period _____

Isotopic Pennies

Application

Purpose:

  • Determine the number of pre-1982 and post-1982 pennies that are contained within the film canister (without opening the canister!)
  • Relate the pennies and the activity to isotopes

Materials:

Sealed & numbered film canister containing 15 pennies

Metric balance

Introduction:

According to Dalton’s atomic hypothesis, all atoms of the same element are identical. This notion of the atoms, however, is somewhat outdated, as not all atoms of the same element possess the same number of neutrons (and therefore possess a different mass). It is in this spirit, that a demonic form of torture, involving pennies, has been selected for you.

In 1982, the composition of pennies changed from being an alloy that was 95% copper and 5% zinc to 97.5% zinc and 2.5% copper. Cents of both compositions appeared in that year.

The task of this lab is to have you determine the number of pre-1982 pennies and post-1982 pennies that are contained within a film canister without opening it. In order to do this, a couple of assumptions will be required. First, there are 15 pennies in each canister. Second, since you are unable to open the canisters, the mass of your empty canister will be provided for you. Third, there will be samples of pre and post pennies available for your use.

Plan:

Explain the process you will use to determine the number of each type of penny. You may wish to consult the required data for some ideas.

Data:

Film canister #______Mass of canister and tape without the pennies (written on tape) ______

Mass of the 15 pennies in the canister ______

Average mass of a penny within your canister (show calculation )______

Average mass of a pre-1982 penny (show calculation) ______

Average mass of a post-1982 penny (show calculation) ______

  1. Determine the number of pre-1982 and post-1982 pennies in your canister. Show all calculations.

Canister # ______

# of pre-1982 ______

# of post-1982 ______

  1. How are the pre-1982 and post-1982 pennies like isotopes?
  1. What is the average mass of a penny in a group of pennies that is 65% pre-1982 and 35% post-1982?

Answer______

CHALLENGE: You have been asked to determine the number of pennies in a roomful of pennies. You have been informed that 89% are post-1982 and 11% are pre-1982. If you were allowed to know only the weight of the entire roomful of pennies, explain how you could determine the number of pennies by using the concept of average mass rather than counting.