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Now that we have a balance, let's explore the differences we might see between coins made years ago and today's coins.
Procedure:
1. Find a handful of pennies. Sort them so that you make two stacks: 1: All those that have dates 1981 or before and 2. All those 1982 and forward. The newer ones are usually shinier, but not always!
2. Place a pre- 1982 penny on one side of your scale and a new shield penny on the other side of the scale.
3. Try this for several pennies and record you data. Which penny is heavier? What does that say about the metal the penny is made of? Would it be the same or different? Which metal would be heavier?
Discussion and Questions
The United States Mint gives information about all coins made in the United States. See https://www.usmint.gov/learn/coin-and-medal-programs/circulating-coins
Doing a little detective work, we found the following information about the current penny:
Specifications of 1982+ Pennies
The penny is not really made of much copper; it is mostly zinc!
With a bit more checking, this is what the reference said about older pennies:
Specifications of 1982- Pennies
Question 1: Does the chart data match your findings in the experiment?
Question 2: Why would a copper coin weigh more?
To answer this question we need to know something about copper and zinc as metals. On the periodic chart of elements, Copper (Cu) is right next door to Zinc (Zn). They have almost the same number of atomic particles are one another, Copper has 29 protons and 29 electrons, Zinc has 30 protons and 30 electrons. You might think that Zinc would be a heavier metal because it has more atomic particles, but no!
When many atoms of Copper are melted together, they fit into a smaller space. Copper has a higher density. That means that more atoms of Copper can fit into an area than atoms of Zinc. If we look at a chart of metals, we can compare Copper and Zinc to one another. The chart shows the weight of each metal for a cubic centimeter--that is a cube that has a measure of one centimeter on each side.
Question 3. What is the density of Copper and Zinc? Which is the heavier metal for the same volume?
Question 4. Why would the U.S. Mint change making pennies from copper to zinc?
Question 5. How would you tell if someone gave you a quarter and told you it was pure silver? How could you test that idea with your balance?
Extensions
Try comparing an old quarter with a new quarter, an old dime with a new dime, an old nickel with a new nickel. Can you determine if there has been a change in what metals are used in coins? Do a search to see what changes have been made over the years.
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