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Copper plating experiment, what is black thing at cathode?

Hi, Yesterday my mom showed me a old saucepan that get broken and it has a little gold plating on it, and she asked me like joking for "can we extract it?", she didn't realize I will go and do what she asking :P and this question made me remember word "electroplating" and made me web search about it.I searched for simple things that I can setup experiment in my home. I found a tutorial about copper plating with simple materials and my curiosity led me to made a copper plating experiment. And I realized I have required components at my home and setup things.

I was have citric acid [on eBay or Amazon] crystals for food purposes.I put handful of that crystals to mortar and converted it to powder. Then I mixed it with a half water filled jar. I found an old transformer which have output of DC 13.3 volts at 1.5 amps. Firstly I dissolve some copper in water, which give it blue color to solution from anode part. In final I successfully plate a coin with copper. But some black "smut" appeared in cathode part. What is it? Is it carbon based molecule that comes from nitric acid? or Copper(II) oxide? Also there is red powder thing appeared in bottom of jar. Which comes from anode. I put that red powder under sun to dry out.(maybe useful later :) )

My Thoughts are: red thing is "Copper(I) oxide" because anode part extracts oxygen from water and it bonded with copper. Black thing is carbon based thing which I don't know (because it makes everywhere black it touches, like charcoal) or poisonous "Copper(II) oxide" which I am afraid of...

I am asking that question because I read things about copper(II) oxide and I see it can be very dangerous, and it make me afraid...

Thanks in advance

Burak Besyuzyetmisbes
hobby - Ankara, Turkey
June 15, 2009

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June 15, 2009

Hi, Burak. Your voltage is much too high and is causing side reactions like hydrolysis of water, 'burning' of the plating, etc. The black smut does not contain carbon; it is very fine particles of copper. I am unaware of copper II oxide being dangerous, although finely divided metal particles are flammable.

Regards,

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

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Hello! :)
I have been running a copper plating experiment for my final year 12 experimental investigation, testing the effect of different concentrations of electrolyte (copper nitrate [affil links]) on the rate of copper deposition.
I have noticed a layer of black sludge forming on the cathode, and I'm not entirely sure what it is and why it is forming!
is it that the copper plating is being burnt due to a too higher voltage or is it the formation of another compound (Cu(II) oxide maybe!?)

I have read another post where the same thing happened, but it didn't confirm that these were the actual substances forming, just that what ever it was wasn't poisonous! :p

Thanks for your help!

Sally H.
Student - Brisbane, QLD, Australia
August 7, 2009