Green pennies

Today we did another fun science experiment. I really liked this one, and Oliver also thought it was pretty neat even though the principles were way over his head. :-)

To do this one, you'll need:
a few bright, shiny pennies
a cereal bowl
a paper towel
white vinegar (about 1/4 cup)

First, Oliver drew a picture of the clean, shiny pennies.


Then he helped me fold the paper towel into a square and placed it in the bottom of the bowl. Next, he poured vinegar on the paper towel -- just enough to saturate it but not leave a puddle of vinegar.


Finally we set the pennies on the paper towel and set it aside. I asked Oliver what his prediction was, and he said, "They'll get really big, from osmosis!" Ha ha ha! I love that he still remembers the gummy bear experiment. :-D


Ten hours later, this is what we found. The pennies were still the same size, but the tops of the pennies were turning green! This is because the copper reacted with the acetic acid in the vinegar to make a blueish green chemical (called carbon acetate, in case you were wondering).


Because the chemical reaction needs oxygen to work, only the tops changed colors. The underside of the pennies were still pristine. :-)