Name:

Lab with Collectible Data:

‘A Penny for Your Isotopes’

Introduction: Isotopes are atoms of the same element that are nearly identical. Each element has a set number of protons or atomic number. Isotopes have different numbers of neutrons and, thus, different mass numbers. When chemists refer to the atomic mass (or atomic weight) of one of these elements, they are really referring to the weighted average of the mass numbers of the isotopes of that element. In this lab you will use pennies to model isotopes. In 1982 the government changed the metal alloy that pennies were made from; therefore, pre-1982 and post-1982 pennies have different masses. You will determine the mass of these two ‘penny isotopes’ and then find the weighted average mass of a penny.

Hypothesis: Make a prediction about which type of penny will be more abundant….

______

Procedures:

  1. Get a bag of 100 pennies. Confirm the number of pennies.
  2. Sort the pennies by date; pre-1982 in one group and post-1982 in another group.
  3. Measure the mass of 10 pennies from each group on a balance.
  4. Calculate the average mass of 1 penny from each group.

m one penny = m ten pennies / 10

  1. Count the total number of pennies in each group and calculate the % abundance of that type of penny in your bag.

% Abundance = (# pennies in group / total # pennies in bag) * 100

Data:

Mass of ten pennies (g) / Mass of one penny (g) / % Abundance
Pre-1982
Post-1982
  1. Using your data, calculate the Weighted Average Mass of all the Pennies in your bag!

Wt Avg Mass = (m pre-1982) (% Abundance/100) + (m post-1982) (% Abundance/100)

Calculations:

Wt Avg Mass = ______


Analysis

  1. Record the Weighted Average Mass of two other groups:

Wt Avg Mass Group ___ = ______Wt Avg Mass Group ___ = ______

  1. Compare your result with the two other groups results: how might they agree or disagree?
  1. Why did you measure the mass of 10 pennies and calculate the average instead of just weighing 1 penny? (there are actually two reasons)
  1. Did your data support your prediction? Explain

Math Enrichment/Challenge Activity:

Isotope Penny Envelope Lab

Students are given an envelope with 10 unknown pennies inside (write mass of empty envelope on outside). They must determine the abundance of each type of penny, pre-1982 and post-1982, without opening the envelope. Activity requires Algebra skills:

(x)(pre-1982 mass) + (10-x)(post-1982 mass) = mass of pennies in envelope