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Electroplating chemical mishap Answered

I figured it would be cool to quickly electroplate some stuff. Since I was lazy, I only used what I had on hand [block of zinc, vinegar, muriatic (hydrochloric) acid)]. The zinc ingot was taking too long to dissolve in the vinegar, so I added about 30 mL of hydrochloric acid. A couple hours later, I was electroplating fine. After two weeks of normal zinc chloride electroplating, the acid suddenly took on a nasty dull brown/yellow amber shade and a ton of white bubbles formed around the zinc (still in the acid). Can anyone tell me what happened?


If this is Muriatic acid purchased in a hardware store make sure it doesn't have stabilizers. I know a lot of people doing the HCl/HOOH method of etching circuits have mentioned that certain muriatic acids with stabilizers cause huge problems.

Also, it could be you are forming copper(I) chloride, which has a deep brown color. This also is often encountered in the HCl peroxide method where the solution goes from green to brown due to the formation of CuCl. The peroxide then oxidizes this to form the proper CuCl2. You could confirm this by adding some peroxide to the mix.

I've done a small amount of plating, and bubbles are normal, i suspect they are from oxides/impurities on the surface of the Zinc. How clean were the parts before you tried plating them?

I wasn't electroplating anything at the time. I left the zinc in because it was still slowly dissolving in the acid. The zinc had been sandpapered before being put in the acid, so it's quite clean. Most of the jobs were just random scraps of copper, so I can't say how clean they were. Still, I hadn't electroplated anything for about 4 days before the reaction, so I don't think impurities are to blame. Any other ideas?