Still got that vinegar we used for our first reaction? It’s going to come in useful again.

Take some vinegar and put it in a jam-jar if you’ve got one, or a glass if you haven’t. Drop a copper coin, preferably an old dull one, into the vinegar and leave it for a few hours.
To stop the vinegar escaping, you’ll need to cover the reaction mixture. That’s where the jam-jar comes in useful, because you can put the lid on. If you’re using a glass, I suggest cling film may be your friend. If the mixture isn’t covered, then the vinegar is going to evaporate, which will first of all make the place smell of vinegar, and second of all stop the reaction from happening. The ethanoic acid in the vinegar is what does the interesting bit, and it will evaporate off long before the water does. You can’t tell by looking whether there’s enough left in solution to make things happen, so best to cover your bases and your mixture.

After a few hours, take the coin out of the vinegar. If everything has worked properly, you should have a nice clean shiny coin. The oxidised salts that dull the surface of the copper will dissolve in acid, exposing new metal.
If you use distilled vinegar, which is clear and colourless, then you may find it has turned a pale blue colour from the copper salts dissolved in it. Pretty, isn’t it?