This is an easy experiment to conduct, but interesting because it involves several chemical reactions and you get some pretty dramatic results.
In this science fair project, you transform dull pennies into shiny ones, then watch them turn bluish-green. At the same time, you can watch rust bubble off of steel nails.
You may have to do some further research to fully understand this project. The basics of the experiment, however, are outlined below.
Place 20 pennies (the dirtier and uglier the better) in a shallow glass bowl containing 1 teaspoon (5.0 ml) of salt, mixed with a quarter-cup (50 ml) white vinegar.
Presto! You will witness a chemical reaction almost immediately. The tarnish on the pennies is called copper oxide and it will react with the weak acid solution of salt and vinegar.
Leave the pennies in the bowl for about five minutes, then remove half of them. Rinse and dry them, and put them on a paper towel marked "rinsed." Then remove the rest of the pennies and, without rinsing or drying, let them dry on another piece of paper towel marked "not rinsed."
Add a steel screw and a steel nail to the bowl containing salt and vinegar. Lean another steel nail against the inside of the bowl so that part of the nail is in the salt solution, and the other part is not.
Wait for an hour, and closely look at all the pennies, the nails, and the screw. You should be able to record a lot of observations and data.
What happened to the pennies that were not rinsed and dried? These pennies actually underwent two chemical reactions: one while they were immersed in the salt solution, and another as they dried on the paper towel.
You know that the reaction was caused by the acid solution. The other occurred when the atoms that make up the penny reacted with the oxygen in the air and the chlorine from the salt. Is there a color change on either of the paper towels? That bluish-green compound that formed is called malachite.
What about the steel screw and nails? How have they changed? What gaseous compound was formed and bubbled through the acidic solution? What would the balanced chemical equation be for the changes you saw?
If you change the concentration of the solution by varying the amount of dissolved salt in the vinegar, you are actually changing the pH of the solution. Test the acidity of each different solution you make using pH paper that tests liquids in an acid range. You usually can find pH paper at a hobby store that supplies science kits and equipment. Do you notice if a change in the pH increases or decreases the reaction rate? Would lemon juice or orange juice produce the same results? Try it and find out.
You can take this project a step further by discussing the chemical changes that occurred in terms of atomic and molecular levels.