Chem 1
Lab Gold, Silver and Melted Pennies
1
Seeing is believing- or so it is said. In this activity
you will observe how the properties of a metal can
be changed. Copper (Cu) , the familiar metal of
pennies, will be changed in properties by heating it
with zinc (Zn) in the presence of a solution of zinc
chloride (ZnCl2 ).
Chem 1
Lab Gold, Silver and Melted Pennies
2
Procedure Part 2: Melting
1. Test the relative melting points of Zinc and copper by holding a New (after 1983) penny, in a
bunsen burner flame. Be sure to tilt the burner so the metal does not drip into it. Only heat the
penny to the flexible point. Not to the dripping point. Cool the penny in the distilled water. Heat
again and cool slowly. Record observations.
2. Repeat step 1 with an old (before 1982) penny. It will respond differently.
Materials: Hot Plate, 250 mL beakers (2), crucible tongs, triangular file.
Lemon juice and salt, Bunsen burner, striker.
Part 1-- 0.5 g finely granulated zinc, Zn; 20 mL 0.5 M Zinc Chloride ZnCl2
solution; Three post-1983 copper pennies, shiny;
Part 2 --- one post-1983 penny, one pre-1982 penny.
3. To a different new penny- use triangular file to scratch off outer Cu layers. Make observations.
Note the thickness of the Cu.
DATA TABLES: Read procedure and make your own inference on data you would require.
Lab ground rules
SAFETY: all later classes should assume that all hot plates and glassware is hot!
The day before the lab: If you want to take the pennies with you, bring your own pennies.
The penny cleaning dishes have lemon juice and salt. They are at every station.
Zinc metal is in little bottles at each balance. Leave the bottles of Zinc at the balances.
The Zinc Chloride solution is at each balance in a clear bottle.
To save time, work on both part 1 and part 2 at the same time.
Create a data table on a separate sheet that tracks observations for three pennies.
Part 1: Changing Pennies to silver and gold
QUESTIONS: Use Complete Sentences!! Do this on your own paper.
1.
2.
3.
4.
5.
3. List some (3 or more) practical uses for the metallic changes you observed in this activity?
Obtain three pennies after 1983. (Clean the pennies in a lemon juice/salt mixture if they are tarnished.)
Weigh a 1.0 g sample of granulated zinc (Zn). Pour it into a 250 mL beaker. (Later classes ignore.)
Carefully pour 20 mL of 0.5 M Zinc Chloride ZnCl2 solution into the beaker. (Later classes ignore.)
Turn on the hot plate, to medium heat. Place a beaker on the hot plate.
Heat the beaker gently until the solution just begins to bubble. Then adjust the heat to continue gently
bubbling. Caution: Do not allow the solution to boil. (spray distilled water if too much evaporates.)
6. Using forceps or tongs, carefully add two pennies to the hot zinc chloride solution. Do not drop the
coins into the solution so that you cause a splash. Set the third penny aside as a control-an untreated
sample that can be compared with the treated coins.
8. Observe and record any changes in the appearance of the coins (they should look silver) until no further
changes are noted.
9. Fill 50mL distilled water 250 mL beaker. Use this to wash and cool pennies.
10. With forceps or tongs, remove the two pennies from the solution. Keep one penny to the side as your
experimental control. Place the two pennies in the beaker of distilled water to remove all lemon juice.
Remove the zinc chloride beaker from the heat, but do not discard the solution.
11. Using forceps or tongs, remove the coins from the beaker of water. Rinse them under running tap
water. Dry the coins with a paper towel. Set one of the treated coins aside to be used for later
comparisons.
12. Gently heat the other treated, dried coin directly in the outer cone of the burner flame, holding it
vertically with the forceps or tongs.
13. Continue heating the coin for three seconds after its appearance changes. Do not overheat it. It turns
gold if you do this right. Immediately immerse the coin in the beaker of distilled water. Record your
observations.
14. Remove the coin from the beaker of water. Dry it with a paper towel.
15. Observe the appearance of the three pennies and record your observations in the table.
16. Empty, rinse, and refill the two beakers with distilled water.
17. Leave the Zinc and Zinc Chloride in the beaker for the next class to use.
DO NOT PUT THE ZINC IN THE SINK!!!!!!!!!!
1. Compare the color of the three coins (untreated, heated in zinc chloride solution, heated in zinc
chloride soluton and in burner flame). Do any of the treated coin appearances remind you of
other metals?
2. How could you verify whether you had changed the copper metal to another metal?
(List at least 3 methods)
4. What happened to the copper atoms originally present in the treated pennies? {Were the copper
atoms used up or destroyed or covered up?}
5. What was the “silver” color made of?
6. What was the “gold” color made of?
7. Explain what you learned about the new pennies vs. old pennies in Part 2.
A CONCLUSION IS NOT REQUIRED FOR THIS LAB!!!!!