There is a lovely experiment where you can plate copper foil (even a coin) with zinc (so it looks like silver although is a dull grey really) and then when heated in a flame, the zinc diffuses into the copper to form brass (so it looks like gold). The method (J. Chem. Educ., 1975, 52 (2), p 102) (http://pubs.acs.org/doi/pdf/10.1021/ed052p102.2) involved boiling the penny in 6M sodium hydroxide solution containing zinc powder. That process is called electroless plating. On heating, brassification takes place as the zinc diffuses into the copper to form the alloy brass, which looks like gold.
This novel experiment, evokes the alchemists dream, However, it resulted in many enquiries to CLEAPSS as Technicians would ask us if students were allowed to use 6M NaOH, never mind boil it. In my role as safety adviser for CLEAPSS, I hate stopping experimentation so I looked for a kinder method.
I tried it with 15ml of 0.4M NaOH with up to 4 g zinc powder heated to boiling and it worked. Elated by my discovery and seeing prizes flowing my way, I thought ought to check the literature again and I found from J. Chem. Educ., 1994, 71 (11), p 996, that it had been carried out in 0.5M sodium hydroxide, http://pubs.acs.org/doi/pdfplus/10.1021/ed071p996.
Scooped again but at least I got it to 0.4M. It can actually work in water, acid and zinc ion solution and acid so long as the zinc is in contact with the copper, but the zinc becomes very clumpy and the result is not as spectacular. I also got the brassification to occur in a spirit burner flame and this stopped further oxidation that can occur in hotter Bunsen flames. So this 42 year old experiment was made safer 23 years ago and I had only just rediscovered it.
The safer version had been lost in publication for over 23 years!
There are also warnings about waste, Filtering the solid zinc powder off and placing it in a bin with paper has been known to cause fires. It is bettter to add sufficient 1M sulfuric acid with a dash of 0,1M copper sulfate solution to dissolve the zinc and leave some copper deposits. These should be disposed according to local rules.
The electroplating method
Therefore, an experiment to be performed “just for fun” can be now an enjoyable exercise with a purpose in teaching electroplating and alloys in chemistry. Necessity was the mother of invention.
Necessity, in a request from our Primary Science Adviser drove me to adapt the conductivity indicators in J Chem Ed (David A. Katz and Courtney WillisJ. Chem. Educ., 1994, 71 (4), p 330 and Set and Kita J. Chem. Educ., 2014, 91 (6), pp 892–897. Here I used robust carbon fibre electrodes (available in kite shops) in place of metal. From just saying “oh that conducts”, I have now found many more uses of this piece of kit.
No doubt all those involved in any kind of research say “Darn it, scooped again!” But with Necessity we can all get little Eureka moments that make it worthwhile. The safety adjustment for electroless zinc plating will now go into CLEAPSS documentation for use by teachers in the UK, although I would prefer that the electroplating method be used a well for educational purposes. Of course by writing this blog I have spread the safety tip to the world but no doubt, it will all be lost in publication.
(I love the word “Brassification”. It needs to said with a strong North England accent! For those of you in other countries who do not understand this, listen to the actor Sean Bean (Game of Thrones) who comes form Sheffield. People in Newcastle upon Tyne in England will now write in and say that Sheffield is not North. You cannot win.)