Link to Penny Chemistry, part 1
Last time, we used a mixture of salt and vinegar to remove the tarnish from pennies. This time, we will get back some of the dissolved copper by collecting it on some iron nails. To try this you will need:
- a small glass, cup, or bowl
- vinegar
- salt
- several pennies
- several iron nails
The start of this experiment is pretty much a repeat of part of last week's experiment. Put a couple of inches of vinegar into a cup. Add a teaspoon of salt, and give it a stir to help it dissolve. This time, instead of dipping a penny halfway into the solution, drop in several pennies.
Very quickly, you will see the same thing happen that we saw last time. The pennies will lose their coating of oxides, becoming bright and shiny. In the process, some of the copper is being dissolved in the vinegar/salt solution.
To get some of that copper back, drop a couple of iron nails into the solution. After a minute or so, you will see tiny bubbles forming on the nails. After an hour or so, look at the nails again. They should have a thin coating of copper.
Why does the copper coat the nails? The solution that dissolved the copper from the pennies is also dissolving some of the iron from the nails. As the atoms of iron dissolve, they leave behind electrons, giving the nail a negative electric charge. Both the iron and copper atoms dissolved in the solution have a positive charge, but the copper is more strongly attracted to the nail, so the copper atoms stick to it, forming a coating.
The bubbles are hydrogen gas, produced by a reaction between the hydrogen ions from the vinegar and the metals. Once enough copper atoms have been deposited to balance out the negative charge on the nail, the process stops.
Does it make a difference if the nail is touching the penny? Try suspending the nail by a string, so it does not touch the copper. Does it still work? To see a stronger contrast, try suspending the nail so that only half is in the vinegar. That part should get a copper coating, while the part above the liquid should remain as it is.
Penny Chemistry, Part 2
I've done this with my science classes. When I left the nail half-in and half-out of the vinegar/salt solution, the part in the solution became copper coated, but after a day or so, a huge pile of black crumbly "something" accumulated on the top part of the nail that wasn't in the solution. I took some of it off and spread it out on a paper towel. It was copper, I think, from the color of it. But it looked black on the nail. Am I right?
Will you be answering this question? If so, here's my email: . I'd like to know.
Thanks!
Susan Coker
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