Editing Penny Alchemy (section)

== Demonstration ==

:Preparation;
* 3M NaOH Solution: In a 1000mL beaker, combine 60g fo NaOH with 500mL of water. It is suggested to use a magnetic stir plate to speed up the process. Once fully dissolved, bottle and label the solution, and store in a chemical cabinet.
* Cleaning the Pennies: For this demonstration to run smoothly, the pennies should be cleaned of any dirt and tarnish on them. To do so, make a 10:1 solution of vinegar and salt in one of the large bowls, being sure that all the salt dissolves. Fill a second bowl with water, and lay out several paper towels. Put the pennies into the vinegar and salt bowl, and you should be able to see them become nice and shiny in 10-20 seconds. Once they are, move them to the bowl of water to rinse them, and then dry them out quickly with the paper towel. Let them air dry as you continue with the rest of the pennies. When dry, bag the pennies and label them for the demonstration.
** Note: <u>'''''Do not clean pre-1984 and post-1984 pennies together!'''''</u> The high zinc content in post-1984 pennies will act as an electrode for the high copper content of the pre-1984 pennies, and can cause a rapid oxidation reaction. You'll be able to tell if there are pennies of different metal contents in the same bowl, as the post-1984 pennies will start to bubble in solution. If not quickly removed, they will start decomposing in the solution, and will tarnish all the pennies near them, if not cause them to decompose as well!
** Additional Note: There will be occasional pennies from 1982 to 1984 that will have zinc centers. This is because the U.S. mint did a transition from full copper to copper-zinc pennies during those years, so you may run into an occasional penny during those years which can cause the rapid oxidation. Keep an eye open for any rapidly bubbling pennies, and wash them in small batches to prevent any problems.

:Presentation;
# Set up: Pour 500mL of the 3M NaOH solution into the 1000mL beaker. Place the beaker on the hot plate and turn it to medium-high. Fill a large bowl with water and set it next to the hot plate. Once the solution starts to steam, put 30-40g of zinc into the beaker, being sure it is spread equally across the bottom of the beaker. Lay out several paper towels off to the side of the bowl of water, away from the hot plate.
# Once the solution is steaming again, you can start placing pennies into it. At this point, it does not matter of you place pre-1984 and post-1984 pennies into the solution together, so long as the post-1984 pennies are not broken and exposing the zinc inside them. Use the tongs to place the pennies gently onto the bottom of the beaker, making sure they don't touch or overlap and are all on top of the zinc.
# After the pennies have been in the solution for about 45 seconds, you can try taking them out. They should be fully silvered over! If not, place them back in the solution and wait an additional 30 seconds. Rinse them with the bowl of water, and dry them on the paper towel.
# To turn the silver pennies gold, place them on the hot plate next to the beaker. Within 5-20 seconds, the penny will start to transition from silver to bronze, then to rose-gold or gold. Once it has finished changing colors, pick it up using the tongs and place it in the water, and it will then become bright yellow gold!
# Allow students to keep either a silver or gold penny. This demonstration is intended to be continuously running during a science night or outreach event, and any extra silver and gold pennies can be saved for later events. Add more water to the solution as needed to keep it around the 500mL mark, and otherwise the solution can be reused several times at later events. See the Safety Precautions section for disposal of the solution.