I got this experiment from Mom to 2 Posh Little Divas. Since I had a character quality lesson I wanted to do with pennies, I thought this would be good accompaniment. We first gathered a bunch of pennies. The older and more oxidized the better. We talked about which one they thought be older or newer based on appearance. I then asked how we could clean them up. Soap and water was the number one suggestion. I suggested water and then another cup of salt and vinegar. I asked them to guess which would clean the best. Soap and water was their choice. So, we set them in the three cups. The salt and vinegar contained 1/2 cup vinegar to 2 tsp. salt. We left the pennies in their mixtures for 5 minutes and then pulled them out. The salt and vinegar ended up being the shiniest, but if not rinsed well turn out more of a bluish green color. Why do they turn this color? The cooper in the penny reacts with the oxygen in the air and salt and turns the penny green. Interesting. Fun little science experiment to learn a little about chemical reactions, hypothesis and the scientific method.