At-Home Science: Penny Cleaning

  by Erik Wolgemuth

Oxidation is difficult to avoid in our world. It’s not so bad once you’ve grown accustomed to Lady Liberty’s greenish-blue, but who really likes polishing off that browned apple? And, for that matter, if we really believe as a society that our copper resources are best used for one-hundredths of a dollar, then I’d contend that they ought to be shiny. It’s upon this subject that our at-home experiment is based.

The ingredients for this experiment are of the common variety – you’ll need a cup, about a half-cup of vinegar, a bit of salt and a penny. What’s key for your penny is that it’s contacted quite a number of oxygen molecules, doing their oxidation work, in its lifespan. If you’ve got a collection of loose change, get your crew to find the dirtiest penny of the bunch. The heavier the tarnish, the better.

Once you’ve found a poor subject or two that needs some sprucing, you’ll want to combine your vinegar and salt in a cup and stir it up to get that salt dissolved. Then, in goes Abe for his wash (a bit of stirring from your young scientists doesn’t hurt). The transformation, while not immediate, does happen rapidly and within a few minutes (you’ll be able to see if things are getting bright and coppery) you ought to be able to remove what appears to be a complete currency transformation. It’s not a bad idea to keep a well-oxidized penny out of your concoction so that you can do a side-by-side comparison of pre- and post-bath. Rinse that cleaned penny in water once you remove it, and award it to your scientists for a job well done.

So, what’s going on? Your vinegar/salt mix combined to form an acid that dissolved the oxide on the copper. Or, the penny got a special wash. Your call.

There’s an extra, rather interesting, step to this experiment if you’ve got a steel bolt or screw (the shinier the better) lying around the house. Once you’ve removed the penny from the cup, keep the liquid and drop in the bolt. The change here also isn’t immediate (though you should see bubbles coming off your bolt) and leaving things to sit for a couple hours is best. What will happen is that your shiny steel bolt will be penny-fied. We’ve entered the atomic-level now, and what’s happened is your bolt attracted copper atoms that were freed from the penny during the vinegar and salt wash. Or, the bolt got a special wash too.


Check out introduction to At-Home Science here. And when the scientific research is wrapped up and it’s time to crash, consider making Tesla or Einstein the hero via the guide to telling bedtime stories.

Picture by JJ; Used via CreateCommons license.