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College Electroplating Experiment Problems

2005

I'm undertaking an investigation into electroplating as part of a 2 week chemistry experiment (aged 17 in the UK). I've been trying to plate copper and zinc cathodes with a variety of metals from solution as part of an electroplating circuit. I've been using 1 volt and (ie) 0.2 molar copper sulphate [on eBay or Amazon]solution along with a copper cathode and carbon rod anode to try and observe the mass change in the cathode from copper ions plating to the cathode.

During the first 2 days (12/1/05 and 12/2/05) I tried to electroplate zinc and copper cathodes with copper sulphate, copper nitrate [affil links], silver nitrate and zinc nitrate in the set up I've described. Some of these have been with 0.2 molar and 0.02 molar concentrations (per decimetre cubed).

The problem I've had is with whats commonly called (or so I've been able to determine) 'burning' or blackening and dis-colouring of the electrodes. At low voltage (1V) the copper grew a black layer which washed away with distilled water to reveal a red-layer beneath (red and black copper oxide?). With the silver nitrate I also got a black layer but believe that this could be fine-powder silver, which has a black appearance. Zinc nitrate also yielded a whiteish layer on zinc electrodes (zinc oxide?) but the strange results don't stop there.

In some of the experiments I noticed a precipitate forming (I'm sure one of these was silver) but in the copper/copper sulphate baths the precipitate tested negative for copper(!?).

I still have about 10 days of experiments ahead of me starting tommorrow and will hopefully learn a little more, aside from any help I can get from here.

Daniel C.
Student - St Helens, Merseyside, UK

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You give a lot of information about what you think you have done, but very little about what you have actually done. There are numerous basic rules in electroplating and the first one is cleanliness. Your electrodes must be clean before you start. If your cathode is dirty, no metal will stick to it. Secondly, most metals will not electrodeposit just because you pass an electric current through a solution containing the elements. You need to have a properly prepared solution with the correct pH and temperature. I suggest you look in a book on basic electroplating, or even look on the Internet for the simplest solutions and conditions, then repeat your experiments. The problem with metals like copper and silver are that they will form immersion deposits if you try to put them onto metals higher in the electrochemical series. These coatings are virtually non adherent and will fall off very easily. Sorry to be so apparently unhelpful, but without actually doing the experiments for you and telling you the answers I think that is the fairest thing to do. The thing about science is the discovery, not the arriving and it is, by its very nature, a practical subject.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005