Summary for copper plating issues Discussion
Copper plating issues in this school electroplating project were traced mainly to using too much voltage and too little dissolved copper. The answerer advised Anna to switch from a 6V battery to about 1.5V because vinegar is only a mild acid and cannot hold much copper in solution; with too much current, water is split instead of copper being deposited, causing the black smut and "burning" she saw. The plating also will not be mirror-bright in a classroom setup because the copper crystals are too large and the surface too rough, though the smut can be rubbed off after plating for an hour. Salt was said to help only by increasing conductivity, and only a tiny pinch is needed. Sugar was not proven to help, though it was speculated it might act like a brightener. The thread also explains that copper acetate forms in solution, and a later question notes that hydrogen is given off at the cathode and oxygen at the anode if bubbles appear there.
I am a seventh grade student who is doing a science project on electroplating. I have used vinegar
⇦ in bulk on
or
Amazon [affil link] (acetic acid
⇦ on
or
Amazon [affil link] ), sugar, and salt. I used a 6V battery as my power source. First I placed both anode and cathode with Copper wire and then once the solution had some copper dissolved in it (color of solution changed to blue), I changed the cathode with a brass washer for plating.
I am getting a black colored and I am wondering why I am not getting the bright color of copper. Also I would like to know how sugar and salt help in the plating process. Can you also help me in getting the chemical reactions (equations) for this experiment.
Thank you,
Anna [last name deleted for privacy by Editor]
– San Jose, California, America
2003
2003
Anna, switch to a 1-1/2 volt battery. vinegar is a very mild acid capable of holding only a small amount of copper in solution. There isn’t enough copper in solution to keep up with the electricity flow from a higher voltage battery, so much of the electricity will cause water to separate into hydrogen and oxygen instead of depositing copper. This results in the smuttiness and “burning” you are seeing.
Your copper plating will not be shiny because in a school experiment the grain size of the copper crystals is too large and the surface too rough to make a mirror-like surface. But I did this experiment myself and photographed the results I got for comparison (see www.finishing.com/faqs/school.shtml). Take your time, plate for an hour, then rub off any smut.
Salt helps by making the solution more conductive. A tiny pinch of salt is plenty. We have not proven that sugar does anything at all. Theoretically it might be a “brightener” that blocks deposition of the copper, interrupting the copper crystals, so more and smaller crystals are forced to form. But we have no feedback from students about whether it really works like commercial brighteners work :-)
Although the exact formulas are beyond 7th grade level–it is too complicated to describe how and why vinegar ionizes in the manner it does– but we do have a simple paper on Faraday’s Law which explains it all.
At the anode the battery steals some electrons from the copper and it becomes a somewhat different material, a positively charged copper ion. These positively charged ions repel each other while also seeking negatively charged ions that can neutralize their charge. The acid is the negatively charged ion and the copper plus the acid form a water soluble copper acetate salt. At the cathode (the item you are plating), electrons coming out of the battery replace the electrons the copper ions are missing, reducing the charge on each copper atom back to zero so the copper can reform as metal rather than ions.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Copper acetate plating
Q. I’m copper plating items with a copper acetate [affil link] solution and was wondering what gas was being given off during the reaction.
Crow Menking
– Simpsonville, South Carolina
January 8, 2019
A. Hi Crow. Hydrogen at the cathode. If there are also gas bubbles at the anode, they are oxygen.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
January 2019