Isotopes and Average Atomic Mass 2013
Purpose of the experiment: In this experiment you are given a film canister filled with an unknown amount of pre- 1982 pennies and post-1982 pennies. Your goal is to determine the number of pre-1982 pennies and number of post-1982 pennies without opening the canister to view the contents.
Materials & Equipment:
Pre-1982 (old) U.S. pennies
Post-1982 (new) U.S. pennies
Empty Container (film canister)
Full container with “mystery” sample of 15 pennies
Balance (analytical or electronic)
Procedure:
1. Acquire all the materials and equipment needed to start the lab.
2. Once all the materials are gathered, record the identification number of your container on its surface.
3. Obtain 10 pre-1982(old) pennies. Weigh them on a balance and find their total mass to the nearest 0.01g ±0.01g. Then use this information to find the average mass of the pre-1982 pennies.
4. Next, obtain 10 post-1982(new) pennies. Weigh them on a balance and find their total mass to the nearest 0.01g ±0.01g. Then use this information to find the average mass of the post-1982 pennies.
5. After you obtain the measurements above, measure the mass of an empty canister to the nearest 0.01±0.01g on a balance.
6. Then, measure the mass of your full canister to the nearest 0.01g ±0.01g on a balance.
7. When you have both the measurements of the empty canister and full canister, subtract the mass of the empty canister from the mass of the full canister to find the mass of the fifteen pennies in the full canister.
8. Use the formulas below to solve for the amount of old and new pennies in the container:
x=number of old pennies; y=number of new pennies; a=average mass of old pennies
b=average mass of old pennies, t=total mass
x+y=15
ax+by=t
(use algebra to solve)
9. Report your results on a sheet of paper, remember to include units and significant figures.