Home /
T.O.C.
FAQs
 
Good
Books
Ref.
Libr.
Advertise
Here
Help
Wanted
Current
Q&A's
Search 🔍
the Site

Chime right in! (no registration req'd)

-----

"Electroplating problems with my science fair project"



 

I'm using electroplating for my science fair experiment. I was wondering if you can give me any information as to why my brass key turned black, when I thought it would be coated with copper. I hooked a strip of copper (with a hole to attach to to a wire) up to a battery, and ran a wire from the other end of the battery to a key. There was an immediate reaction, and after an hour, the key that was submerged in a vinegar/salt solution was covered with... something black, that could be scratched off with some effort. I'm in 10th grade, this is for my Chem class

John C [last name deleted for privacy by Editor]
- Huntington Sta. New York
^


 

My first thought is that the 'immediate reaction' you saw was excessive gassing from a voltage that was much too high. Tell us you used 1-1/2 volts, or tell us you're going to try again at 1-1/2 volts. 12 volts would be much too high. The other problem is that you may have had the current reversed. The negative pole of the battery attaches to the piece you want to plate.

Please see our FAQ about How Plating Works for some additional details for the experiment. Good luck.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


 

No, it was a 1.5 volt, D-sized battery. And the key was attached to the negative end. I'm somewhat skeptical if the "copper banding" if indeed pure copper. Upon closer inspection, it was black (on the inside) where I had cut it. Do you think that the black... substance inside the key was responsible, or is it possible that electroplating copper on brass makes it black in color?

John C [last name deleted for privacy by Editor]
- Huntington Sta, New York
^


 

Copper plating on brass should be copper colored. If it's not, something is wrong. But it's not uncommon to use too high a voltage, or put the plated part and the anode too close together. This makes more current flow than the copper ions can carry, causing the generation of too much hydrogen from the water, or forcing the copper to deposit as tiny black specs instead of building a proper crystal structure. This black smut is called 'burning'.

You may be right that your anode is not copper. Although I don't think that's the cause of the black smut, just get some copper wire for use as an anode -- that's very pure copper.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


 

Alas, ted, the answer resides in the counter ions he used for the bath. Salt and acetic acid make for an interesting mix that will certainly boost conductivity, but they hardly are acceptable anions for trying to plate copper from. His hydrogen overpotential at the cathode is so reduced by the presence of the acetic acid that it will burn at .125 VDC. The resultant hydrogen will then form hydrochloric acid and etch his surface further, pushing the overpotential further and further away. You're right he burned it, but its the solution that is the problem!

tom baker
Tom Baker
wastewater treatment specialist - Warminster, Pennsylvania
^


 

Vinegar plus salt is certainly not a suitable industrial plating electrolyte, Tom, you'll get no argument about that. But this is for a school science fair where safety is paramount. And the fact is, you can get a thin but decent copper plate out of this solution for science fair purposes.

The acid is so weak that the amount of copper in solution is very limited (you'll hardly see the faintest blue tint), but I've used it to plate things (like quarters) where even a very thin plating will show very quickly and I plated a brass key that you can see in the FAQ; it held up to light wear for several months. I suggest that John plate a quarter first, and after he has that down, he can see what happens with his brass key.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


 

I was able to obtain a pure copper strip from my science teacher. I got better results. While it was still largely black, it had a copper tint to it. I also tried this experiment with a chrome-plated brass key. The key went from a shiny silver color to a total black (but it was a covering) , AND the copper strip had a coating of chrome on it. I'm VERY sure that I had the key hooked up to the negative side of the battery. Thank you very much for you help. Do you mind if I quote you in my report that goes along with my science fair display?

John Costello
- Huntington Sta. New York
^


 

John, it will only cost you a quarter to try what I suggested :-)

The first step in building onto a successful experiment is to repeat what we know worked so that we know the solution and anode and polarity are okay. Instead, you've introduced still another variable (a chrome plated key). To be trying step 2, plating a brass key; and step 3, plating a chrome plated key before you've tried the quarter may be wasting time.

What you are seeing on the copper strip is absolutely not chrome because it is impossible to plate chrome under these conditions--but we are totally off on another tangent already! The negative side of a 1-1/2 volt battery is the bottom; the positive side is the raised pimple on the top. Are you sure the anode and cathode are not touching?

Sure you can quote me; I generally got B's and C's in high school, and it would be nice to be associated with an A :-)

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


 

I've not tried it, but the obvious choice for a soln to try would be a copper sulfate [affil. link to info/product on Amazon] soln with a little battery acid added, look at this reference, it may give you some ideas www.courseworkbank.co.uk/GCSE/Chemistry_Coursework/Electrolysis/ as with all plating the work must be CLEAN to have any chance of success, scrub it with a say a bath or sink cleaner, well rinse, without touching too much of the surface.

Best of luck,

David Hext
- Edinburgh, Scotland
^


February , 2008

No question that copper sulphate and sulfuric acid is a much better plating solution, David. An issue, though, is what is safe to display at a science fair.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


March 1, 2008

My son wants to do an electrolysis science project; he wants to clean pennies using electrolysis or reverse electrolysis. We have read of dangers of toxic gases being released and/or dangerous metal compounds ending up in the electrolyte depending on what is being used. He was going to use a solution of water and Arm and Hammer Washing Soda, and a steel nail on the positive. Can you tell me what gas is being released and if it is safe? Would you recommend this solution and cathode (not sure I got that right) or another?

Joe Mulvey
- Marlboro, MA USA
^


March 1, 2008

The only gasses evolved from your son's experiment will be hydrogen at the cathode (the positive pole) and oxygen at the anode (the negative pole), which are non-toxic; but there is just no saying that it is impossible to have an accident that ignites this small amount of hydrogen. We can all be run over by the proverbial truck at any time, Joe: there is no such thing as safe. But I'd be more concerned about the electricity: not more than 6 volts.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^

none
finishing.com is made possible by ...
this text gets replaced with bannerText
spacer gets replaced with bannerImages

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

 
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g, Train'g
& Software


About/Contact    -    Privacy Policy    -    ©1995-2021 finishing.com, Pine Beach, New Jersey, USA