Making Gold Pennies

MAKING “GOLD PENNIES” Name ______

Background: The ancient alchemists sought to understand nature and carried out many experiments which furthered knowledge of dyes, glass making, metallurgy and medicine. One of the many things the alchemists worked on during the Middle Ages was trying to turn base metals into gold. Their work was often misunderstood and they were often forced to work in secret, leading to even greater misunderstanding of alchemy. You can find more information at:

http://en.wikipedia.org/wiki/Alchemy http://www.levity.com/alchemy/home.html http://www.ambix.org/

Safety:

Sodium hydroxide (NaOH): Sodium hydroxide is caustic and extremely harmful to your eyes —it can blind you. In this lab, it will be boiling, so it is even more harmful. Do not touch it or splash it when putting your pennies in it. If you get any on your skin, rinse thoroughly with plain water (not soap) and tell the teacher.

Zinc dust: powderized zinc is extremely reactive. In this lab, it will be mixed with the NaOH solution. If you have to rub some extra zinc off of your penny with a paper towel, the zinc could cause your paper towel to catch on fire, even several minutes later. Keep any paper towels with zinc on them away from other papers and wet them if they begin to smolder.

Bunsen Burner: Keep all papers away from your lit Bunsen burner. Follow all safety rules covered at the beginning of the year.

Pre-Lab Questions:

1) Name 2 safety concerns about NaOH.

2) Define these terms:

a. Alloy

b. Etching

c. Galvanizing

d. Brass

e. Bronze

f. Caustic

g. Corrosive Materials: - Goggles - Pennies - Bunsen burner - Hot plate - Steel Wool - 1 M HCl - Clean beaker - Graduated cylinder - 6 M NaOH

Procedure—Part 1—Making Gold Pennies

1) Put on your goggles and keep them on for the entire lab. 2) Get 1 penny per person. Everyone must turn in his or her own gold penny. 3) Put about 10 mL of hydrochloric acid (HCl) in a small beaker. 4) Place your pennies in the acid to clean them. This will remove any copper oxide coating and other dirt. Keep them in the acid for about a minute. 5) Rinse the pennies thoroughly by running tap water into the beaker for 1 minute. Then take the pennies out with tongs. 6) Lightly rub the pennies for about 5 seconds (on both sides) with steel wool. This will roughen the surface and give the zinc a better chance to adhere to the copper surface. Don’t get steel wool dust into your eyes. 7) Using tongs, place your clean pennies into the Zinc dust/NaOH solution at the fume hood. CAUTION! This solution can blind you and has harmful fumes. Don’t splash or spill. Leave your penny in the zinc solution for several minutes, or until it turns completely silver. It is now galvanized. 8) Remove your penny with tongs and place it in a plastic weighing dish or a beaker. Rinse it thoroughly with water. 9) If there are clumps of zinc powder on your penny, rub it off with a paper towel. 10) Prepare a beaker of tap water for the next step. 11) Do not over heat your penny in this step! Holding your penny with tongs, wave it gently over a Bunsen burner, heating both sides evenly. As soon as you see the whole penny change color, take it out of the flame and drop it in the beaker of water. (This is called “quenching”). 12) The penny is now cool enough to touch. Congratulations! You have made brass, an alloy of copper and zinc. Hand it in to your teacher!

Procedure—Part 2—Making Hollow Pennies

1) Get one new penny per group of 3-4 people (new = 1983 or newer, so it is zinc-filled) 2) Using a metal file as shown by the teacher, make 3 nicks around the edge (small, but deep enough to expose the silvery zinc). 3) Put about 30 mL of HCl into a small beaker. Put your group’s pennies in it. 4) Observe the bubbling—the zinc is reacting with the acid and dissolving, but the copper coating will remain in place. 5) Put a label on the beaker and turn it in to the teacher—the reaction will take a couple days. Questions:

1) Write the reaction for what happened when the file-nicked penny reacted with the HCl in part 2. Include states of matter. Using the activity series, (remember that from way back when?) explain why the zinc reacted but the copper did not.

2) List 3 common properties of metals.

3) You defined “alloy” in the pre-lab. What is the advantage of an alloy over pure metals?

4) Look up 5 examples of real alloys and describe what they are made of. For example, your “gold” penny was really brass, which is an alloy of copper and zinc.

5) Look up one of the following alchemists and write a one-paragraph summary of what he or she did. (Jabir ibn Hayyan, Rhaes, Ko Hung, Sun Po, Hermes Trismegistus, Arnold of Villanova, Geber, Paracelsus, Bottger, Hennig Brand).