Copper plating nail experiment

A. Which "copper plating nail experiment" was that, Gerald? I don't think that one is here, and believe you are referring to some other experiment that I wouldn't know the details of.

I believe best voltage is 1-1/2 volts, but I think you should try plating a quarter or a dime rather than a nail. The cause of the black smut is the application of more voltage than the solution can sustain, which results in countless little particles of copper depositing on the cathode, instead of a proper crystal structure being slowly built. Good luck.

Please see our FAQ: "How Electroplating Works"
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
 

A. Hello Janet,

The biggest reason not to use a galvanized nail is that the plating will proceed without the application of any electricity, via immersion plating. Check your other lesson plans and you may well find one that calls for immersing a nail in copper sulphate and watching it plate itself. Your experiment will be a disappointment when the kids realize that the plating did not require electricity and the batteries and wires and such were just "props". If the nails are plain steel, immersion plating will still occur; and if they are zinc galvanized, it will happen all the faster and more obviously because zinc is such an active metal.

Pennies and dimes, being cupro-nickel alloy, are very similar to copper in electroactivity, so immersion plating should not occur, and the amount of plating will be proportional to the amount of current applied, in accord with Faraday's Law. Plus, the copper coloration on a shiny dime or quarter will also be much more impressive than on a nail.

Lemon juice will work, but white vinegar is water clear, with no pulp and pits to contend with and of reliable strength. Plus it is a "real" reagent--mild acetic acid--because its chemical composition is simple and controlled. Lemons have both citric and ascorbic acid (which one was important for plating?) Their strength would depend on ripeness, origin, size, and other factors, and there are hundreds of extraneous trace chemicals in the juice of a lemon. Science is best conducted with controlled variables, rather than with the injection of extraneous, unknown, and undeterminable factors into the experiment -- which might in the worst case make the experiment completely unrepeatable. Good luck!

A. The electrons flow through the battery and wires from the positive (anodic) pole to the negative (cathodic) pole, Adam. So the nail will have an excess of electrons accumulating on it. The shortage of electrons at the anode produces positively charged ions which dissolve into the solution and migrate from the positive pole and flow to the negative pole to balance the charges. That movement of these positively metal ions through the solution, and their reduction onto the cathode is what causes the plating to occur.

A. Hi, Joanna. Did you use a single 1-1/2 volt battery as suggested? Did you electroplate onto scrap first, per our FAQ, until the solution had at least a slight bluish color?

As previously mentioned, copper dissolves into ions at the anode (positive pole) which travel through the solution to the cathode (negative pole) to try to keep up with the electrons which the battery is pushing from the anode to the cathode.

If the voltage is too high, or there is too little copper dissolved in the solution, there will not be enough copper ions at the cathode to match the electrons, so undesirable side reactions start happening to consume those electrons.

Regards,

A. Hi, Patrick. I don't have knowledge of why the nail ought to be copper plated (why not a stainless steel nail?), but if it is to be functional, you should probably buy copper plated nails rather than try to make them. Electroplating is an industrial science, and the copper plating that we are speaking of on this page is for a science demonstration not functional use. Good luck.

Regards,

A. Hi Sarah. I don't know why kids continue to use 6 volt batteries instead of 1-1/2 volts, when it destroys the experiment -- as you have discovered, and as as we've been saying here since 1995 :-)

If the dime was "touching the penny", it was "attached" to it. But if it was forgotten and you didn't see it, are you really sure it was touching it? Or are you jumping to the conclusion that because it acquired a copper coating it must have been touching? Jumping to conclusions and then trying to explain them can be bad science :-)

I suspect that the dime was not touching the penny and that it got plated because it acted as a bipolar electrode. Remember that electrons are flowing through the wires and batteryfrom the anode to the cathode and that, to balance that, positively charged ions are migrating through the solution from the anode to the cathode. But liquids do not carry electricity nearly as easy as metals, so if you afford a metallic "short circuit" somewhere between the anode and the cathode (like a dime in the pathway), electrons will flow through the dime towards the anode so the positively charged ions don't need to travel as far to balance the charges. So see if this explains what happened: The dime was in the solution, in between the screw and the penny. Because one end of the dime was closer to the screw than the other end, electrons flowed from the screw end of the dime to the penny end, and these electrons reduced copper ions in solution into copper metal at the end nearest the penny.

Regards,