“Gold” Penny Lab
How much is a penny worth? “One cent” is certainly correct, but then again maybe it’s not. It all
depends! Confused? Read on.
A PENNY FOR YOUR THOUGHTS? Consider this article:
Zinc Made More Cents
By Karen Chapman Staff writer for the Alexandria Post
After remaining largely unchanged since the first release in 1909, the Lincoln Head penny lost a full
20% of its mass in 1982. The change (no pun intended) was a money-saving measure. Less expensive and
lower density zinc was substituted for some of the original copper. Copper prices had risen so much that the
copper in a penny was worth more than one cent. The pre-1982 pennies were 95% copper and 5% zinc.
Current pennies are 97.6% zinc, coated with a thin copper layer.
When a coin’s material value becomes greater than its face value, two undesirable things can happen.
First, the U.S. Treasury loses money in manufacturing the coin. When the content of the penny was changed in
1982, it was estimated that the United States would save $25-50 million annually. Second, individuals may
remove the coins from circulation, selling them – at a profit – for their metal content.
In light of this information, how much is a penny of today really worth? As in the case of pennies,
chemists are often asked to find way to substitute less costly, more plentiful resources for scarce and
expensive ones, without sacrificing key advantages of the original materials. The new pennies are almost as
durable as the old pennies, because the hardy copper plating protects the more chemically active zinc from
the wear and tear of daily use.
As suggested, “worth” of coins has at least two meanings. If the values of the metals in a coin are considered,
a penny may be, depending on the current market value for the metals, worth more or less than one cent. As
money, of course, a penny is still just a penny. The U.S. Mint is able to make what is essentially a zinc coin look
like a “copper penny.” Let’s see if you can use some chemistry to alter the appearance of a metallic coin.
PENNY LABORATORY ACTIVITY
PURPOSE:
To investigate one method in which a mixture of metals (alloy) is formed
To observe how the properties of the metals making up the alloy are changed
DISCUSSION:
After reading the article “Zinc Made More Cents”, you should have an understanding of why the composition
of the Lincoln Penny was changed and know the approximate percentages of copper and zinc in both the pre82 and post-82 pennies, but how is the copper metal able to adhere to the zinc metal on the inside of the
penny?? In this lab you will perform an experiment that shows one technique of getting metals to “stick”
together. You will be creating an “alloy”. An alloy is simply a mixture of metals. Brass is a mixture of copper
and zinc, bronze is a mixture of tin and copper, stainless steel is a mixture of iron and chromium, to name a
few. Recall from the matter classification diagram that a mixture is a matter with a variable composition and
the components can be easily separated by physical means. In an alloy, the amounts of metals can be
changed, just like the pre-82 pennies have more copper and less zinc and the post-82 pennies have more zinc
and less copper. In this lab activity, let’s see if you can change the amounts of the metals contained in a penny
and if its properties are changed.
MATERIALS/EQUIPMENT:
Balance, 3 shiny pennies, 100, 150, and 250 mL beakers, small and medium iron rings, ring stand, burner,
matches, wire gauze, watch glass, stirring rod, 25 mL graduated cylinder, forceps, crucible tongs, granular zinc,
and 1M ZnCl2 zinc chloride solution.
PROCEDURE:
1. Put on safety goggles and lab apron.
2. Obtain 3 pennies and record observations in Table 1, below.
3. Assemble a ring-stand with iron rings and wire gauze. The medium iron ring goes underneath the small
ring which is used to support the 150 mL beaker. See Figure 1, below.
.
Figure 1. Setup for reaction between zinc and zinc chloride.
The beaker rests on the wire gauze and is prevented from
tipping by a ring clamp of the proper size.
4. Carefully weigh approximately 1 gram of granular zinc into a clean and dry 150 mL beaker. **NEVER
WEIGH CHEMICALS DIRECTLY ON THE BALANCE PAN!!!**
5. Place the 150 mL beaker inside the smaller iron ring for support.
6. Very carefully measure 20 mL of 1M ZnCl2 zinc chloride solution in a graduated cylinder and transfer it
to the 150 mL beaker that contains the zinc. Caution: The product in the test tube, zinc chloride (ZnCl2),
is a severe skin irritant. Avoid direct contact. If it spills or splashes occur, wash the area with plenty of
water.
7. Heat the beaker and contents gently with the burner just until the solution begins to bubble. Lower
the flame so that the solution continues to boil, but very gently. **DO NOT ALLOW THE SOLUTION TO
BOIL VIGOROUSLY, AND DO NOT INHALE THE VAPORS!!!**
8. Using forceps, carefully place 2 pennies in the hot zinc/ ZnCl2 zinc chloride solution solution. Do not
drop the pennies in!! The 3rd penny is a “constant” for comparison. The other 2 pennies are the
“variables”.
9. Stir the pennies gently and carefully every few minutes.
10. Fill the 250 mL and 400mL beakers about one-quarter full of tap water.
11. After 5-9 minutes, or when the pennies turn silver, turn off the burner.
12. Remove the pennies from the solution using forceps and gently place 1 into each of the 250 mL and
400 mL beakers. This is to cool the pennies and to also remove traces of the ZnCl2 zinc chloride
solution. Do not discard. Record observations in Table 1, below.
13. Using forceps, remove the pennies from the beakers, place on a paper towel, and gently dry.
14. Relight the burner and using the crucible tongs, hold 1 of the pennies on the edges and briefly move it
back and forth through the outer cone of the flame as shown in Figure 2. *DO NOT ALLOW THE PENNY
TO REMAIN IN THE BURNER FLAME FOR VERY LONG, IT ONLY TAKES A FEW SECONDS*
Figure 2. Heating zinc-zinc chloride
treated coin. The coin should be heated in the outer cone of the burner flame.
15. As soon as a change is observed, remove the penny from the flame and place it into the empty beaker
of water. Remove the tongs and dry. An alloy has just been formed! Record observations in Table 1,
below.
16. Repeat steps 14 and 15 for any remaining silver colored pennies or leave them silver colored.
CLEANUP:
17. Discard the tap water from the 250 mL and 400 mL rinse beakers into the sink.
18. Discard the ZnCl2 zinc chloride solution from the 150 mL beaker into the liquid waste container
provided by the teacher. Rinse any remaining solid zinc into the solid waste container using a water
bottle. “NO ZINC IN THE SINK!!”
19. Clean all lab ware thoroughly and return it to the designated location.
20. Clean the lab station and remove safety goggles and apron. Wash hands thoroughly.
21. Zinc chloride (ZnCl2), is a severe skin irritant, however, If the gold and silver pennies are rinsed with
excess water, they may be taken home.
Data Presentation:
Table 1. Observations.
Observations
Pennies before heating (Step 2)
Pennies after heating in ZnCl2 solution (Step 12)
Pennies after heating in the flame (Step 15)
Conclusions:
1. Classify the changes to the pennies as either physical or chemical changes. Cite evidence from Table 1
to support this claim.
2. What 2 metals do the treated pennies most resemble?
3. How could someone prove or discredit the claim the gold colored pennies were really gold?
4. Name one use in everyday life for the metallic changes observed in this lab.
5. What happened to the copper atoms on the outside of the treated pennies?
6. Explain at least 2 ways for getting the treated pennies to look like the untreated control penny.
7. List at least 2 advantages of using an alloy rather than a pure metal.
Report requirements for this lab:
1. A neat and organized copy of Table 1 including observations.
2. Responses to Conclusion questions written neatly in complete sentences.
3. Neatly written is acceptable, typed is also acceptable.