Penny chemistry - Verdigris and copper plating

Lesson: Copper plus oxygen creates copper oxide (2Cu+O₂-->2CuO )
What Happened: Changing the chemistry of pennies and nails changed their color

Anthony (perhaps inspired by a discussion of the construction of the Statue of Liberty in history this week) wanted to see if he could make a penny turn green by soaking it in water. I suggested we also try vinegar. Nothing very dramatic happened, so I looked it up and found this great demonstration on About.com's Chemistry page:

1. First we mixed 1/4 cup vinegar with 1 teaspoon salt.
2. Next we dipped one dull penny in for 10 seconds, making it half shiny.
3. Then we dumped about 20 dull pennies in the solution for 5 minutes.
4. When the pennies were removed, some were rinsed with water, the rest left to dry as is. Within a couple of hours, the vinegary pennies had developed a nice verdigris finish.

But here's the best part. Once we took out the pennies, we put some steel nails (I couldn't quite tell if they were galvanized -- zinc-coated -- or not) in the vinegar. Over the next few hours, the nails got a beautiful copper coating. Here's Anne Marie Helmenstine's explanation of what happened: The pennies react with the salt/vinegar solution, releasing positively charged copper ions. The vinegar also dissolves the iron and oxides on the surface of the steel nail, giving it a negative charge. The positively charged copper ions are more strongly attracted to the nail than the iron ions, so a copper coating forms on the nail.

During the process, the hydrogen ions from the vinegar (acetic acid) and the metal/oxides produced bubbles of hydrogen gas.

Although it took longer than advertised, the end result was impressive. Most impressive was finding a way to do copper plating without using CuSO4 (one of the caustic copper sulfate experiments from Joy of Chemistry that I had been avoiding doing).

Update: Works on paperclips, too!

Here's a site that gives all the chemical equations involved.