Iron nail in magnesium sulphate and vinegar

What is the role of magnesium sulphate and vinegar ⇦in bulk on eBay or Amazon [affil link] in the plating of iron when we immersed the iron nail in the mixture of vinegar and magnesium sulphate the iron nail formed dark area?

Hi there! we conducted an experiment in school about plating a copper penny without using electricity. We mixed vinegar with magnesium sulphate and soaked the penny and an iron nail for two days. I'm just curious, why do we need to add magnesium sulphate in the solution? what can it do on the penny? what is its role in the plating process?

Thanks!
bye the way, your site is great! (^_^)

Thanks for the kind words, Kristine.

Magnesium sulphate is simply a salt that can provide ions (Mg+ and SO4-) to improve conductivity. Pure water conducts electricity poorly, and electricity must flow in order for copper to plate on the nails. Because the vinegar can also provide ions, I am not sure if the magnesium sulphate improves things or not. So there's a good experiment for you: demonstrate that the magnesium sulphate helps or does not help.

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