Plating Coins
Recently, a man bought a coin he thought was gold. He spent $84,000 on this coin! A real gold coin is pictured at left, the fake gold is pictured on the left. The fake gold coin was plated silver so only contained a tiny amount of gold. How did they make this coin look gold? In this exploration students will turn silver-colored coins to copper.
Required Materials
• Pre-1982 penny
• Nickel
• 9 volt battery
• 2 wires (these can be any sort of small wire. A discarded electronic device will have wires that could be used.)
• Root Killer (Make sure the label says: Copper Sulfate) You do not need very much so check your neighbors--maybe someone has this already on the shelf.
• Small cup
• Salt and vinegar
• Duct tape or any strong tape.
Procedure
1. Place a small amount of root killer (copper sulfate) in a cup of water.
2. Make a solution of water and the copper sulfate. Mix the granules until you make a deep blue solution.
3. Clean a copper penny and a nickel with salt and vinegar until they are clean.
4. Prepare two wires by removing any plastic insulation from each end. You can use a utility knife, scissors, or other tool to remove the plastic.
5. Make a small loop on the end of each wire and tape it to one side of each coin. Make sure the tape presses on the coin so that the wire makes a good connection to the metal.
6. Attach the wire from the nickel to the side of the battery that has the minus sign (the negative of the battery.) Connect the penny wire to the plus (+) side of the battery. You may need to tape the wire to the battery.
7. Place the coins and their wires into the copper sulfate solution. Allow it is sit for one minute.
8. Remove the coins. Clean the nickel with a soft cloth. Here's how ours looked! The one from our experiment is on the left and a regular nickel is on the right.
Question: What do you think happened to the nickel? Where do you think the copper that is now on the nickel came from?
Discussion
What you have done in this experiment is "electroplate copper on the surface of the nickel. Electroplating uses the concept of electrons moving through a liquid. In the diagram below the orange rectangle represents copper and the fat "c" shaped objects represent copper atoms. The pink rectangle represents the nickel. The blue green is the solution of copper sulfate. When a battery is connected, electrons are pulled from the copper to the battery. The atoms of copper are then attracted to the negative of the nickel.
The solution of copper sulfate allows the copper atoms to move easily in the liquid.