This guide will show you how to transform boring old pennies into shiny silvery wonders! The method of choice is, in this case, electrochemistry. Specifically, this Instructable will use electroplating to put the shine on your moolah. In other words, we will coat a normal penny in a thin layer of zinc metal and then shine it to a sparkle.
This is an alternative method for making silver pennies. Other methods include:
As for difficulty, this experiment is fairly easy and can be completed with stuff you've most likely got at home. After the overnight preparation, this experiment will take less than an hour. Enough talk, let's begin!
Step 1: Bill of Materials
As stated above, you really don't need much to do this fun chemistry experiment. You might even have everything at home, right now. You will need:
Step 2: Making the Electroplating Solution
This is the liquid that you will put your pennies in to plate them in zinc. To make it, fill your beaker or glass with vinegar; the amount doesn't really matter, but you should fill your beaker to about a half inch to an inch of the top. Next, add in your zinc metal. For this step, you can use either powdered zinc or solid zinc blobs, ingots, or shot. Powdered zinc might work faster, but zinc ingots/blobs work just fine. Leave your solution overnight. The vinegar (acetic acid) will dissolve some of the zinc metal, making zinc acetate. Keep in mind, though, that this does not mean there are zinc acetate molecules floating around in your solution. There are zinc ions (positively charged) and negatively-charged acetate ions, but they are not really connected. After you have left your solution to sit overnight, remove the zinc metal and proceed to the next step. The solution should still be pretty much clear.
Note: If you use powdered zinc, you will need to filter the solution through a coffee filter to get rid of the zinc, where if you use solid zinc blobs, you can just remove them with fingers or tweezers, or something of the like.
Step 3: Prepare the Pennies
Your pennies should already be fairly clean and shiny, but they aren't clean enough! Even finger oils will hinder the electroplating process. To clean the pennies, use a wire wheel on a Dremel tool and brush the pennies on both sides. You could also probably use a wire brush, or if your pennies are really shiny already, an old toothbrush with some soap. Now put some alcohol on the paper towels and wipe the pennies off some more. This will get the oils off the coinage and make them yet shinier and cleaner. Try not to touch the pennies with your bare hands now. Use a clean paper towel, or some tweezers.
Step 4: Electrocute the Pennies!
Now you're ready for the fun stuff! Attach one alligator clip to your clean penny and fully submerge this in your electroplating solution; you can use the tape or clothespin to hold it in place so it doesn't flop around. Next, grab a piece of solid zinc metal and attach your other alligator clip to this. Place the zinc in the solution, opposite the penny, and secure it in place, but don't let this alligator clip touch the bath. The zinc metal is eaten away in the process, and your alligator clip will be too, if you aren't careful! Next, attach the penny's clip's other end to the negative on your 3.3V power source. When you're ready to begin the electroplating, attach the zinc's clip's other end to the positive and turn the power on, if necessary.
Note: when I tried using 2 AA batteries in series as the power source, nothing happened at all. However, when I used my lab power supply with the 3.3V line, the penny turned silvery grey immediately. I don't quite know why the batteries didn't work.
While you let the pennies electrocute, here is a little science: The zinc ions talked about previously are what allow the zinc metal to go from the positive electrode (the zinc blob/ingot) to the penny. Without them, the electroplating would most likely not work. The electricity, on the other hand, provides the energy to move the zinc to the copper. Zinc, being more reactive than copper, would not, under normal conditions, attach to the copper.
Now you're really electroplating! When you see a uniform grey layer on the penny, remove the coin from the solution using tweezers and rotate it in the jaws of the alligator clip, then flip the penny so it faces the zinc metal with its other side and re-attach it in the solution. This ensures that all areas get a uniform coating of zinc metal. Keep this up until the whole penny is thickly covered in the grey; then remove power, wash the penny in water, and dry it off.
Step 5: Cleaning up
Your penny is electroplated! It probably doesn't look like much though, so you should clean it up. Use the same Dremel tool with a wire wheel to brush the surfaces of the penny shiny. Don't hold the wheel in one spot too long, or you will scuff the shiny zinc. Depending on how long you let the penny plate and how much you cleaned it in step 3, you will now have a medium-to-high strength plating of shiny zinc! If you want, you can go further by using a buffing wheel to really bring out the shine on your new coinage!
If you are adventurous, you could try to pay for something with this, but I will not advise for or against doing so.
I would like to note that this silver penny has a thicker layer of zinc than is achieved by other silver penny experiments. Thus, turning this silver penny into a gold penny by heating it does not work (I tried multiple times). The upside of this method is that the zinc plating is fairly heavy duty, so you could carry this in your pocket and the zinc wouldn't wear through. That said, enjoy your silver-colored penny and have fun admiring its awesome shininess!