How to isolate the copper shell of an American Penny
Note: This only works with post-1982 American pennies. Before 1982, the American penny was made of pure copper. In 1982, the U.S. government altered the composition of the penny to copper-coated zinc due to the high cost of copper.
This procedure requires a wait period of 24 hours.
You will need:
1. Using a metal file, scratch several deep marks into the edges of a post-1982 penny to reveal the zinc underneath. The zinc looks like a shiny silvery metal.
Note: Do not be overzealous in your filing, or your copper shell may split in half after the zinc has been dissolved. I learned this the hard way when I did this in class. To make matters worse, I dropped the tails end into the sink and accidentally crumpled it while fishing it out. Abe also appeared to have some weird stains on his face.
2. Place the post-1982 penny in a 100 mL beaker (or another glass lab beaker of some sort). Carefully add 30 mL of 6 M HCl. Place the glass cover on top of the beaker. Leave the beaker sitting in a safe place (preferably under a fume hood, away from flame) overnight.
Note: Upon placing the penny in acid, bubbles will immediately form.
Once the penny sinks to the bottom of the acid, the bubbles will be visibly rising from the grooves you have etched in the penny. The bubbles are hydrogen gas (H2) that come from the reaction of zinc with hydrochloric acid (HCl).
Warning: Do NOT leave the penny in acid longer than 24 hours. After 24 hours, a slow redox reaction will dissolve the copper.
3. Remove the penny with tongs (don't squeeze!) and carefully wash it with water. Shake out any excess water. Rinse the penny with ethanol (or acetone) to remove all traces of water. (The reason for this is that ethanol and acetone evaporate much more quickly than water.) Squeeze the penny gently to remove the ethanol and dry with a paper towel.
Note: Chances are you will have black chunks of solid at the bottom of the beaker. The black solid is simply impurities in the zinc.
4. Neutralize the acid with sodium bicarbonate (NaHCO3) and discard.
Congratulations! You have isolated your copper shell!
The chemical reaction demonstrated with this procedure is as follows:
Zn (Zinc) + 2HCl (hydrochloric acid) ---> ZnCl2 (soluble zinc chloride) + H2 (hydrogen gas)
This is a simple single-replacement reaction.
At this point, you may be wondering why the acid reacts with the zinc but not the copper. This reason for this is that Zinc is higher on the activity series than Copper. At the bottom of the activity series are the jewelry metals, which are (in order from most active to least active) Copper, Silver, Platinum, and Gold. Copper cannot displace hydrogen in a reaction, but Zinc can.
This procedure was taken from personal notes as well as a lab writeup I prepared for class. A similar procedure can be found at http://matse1.mse.uiuc.edu/~tw/metals/f.html