Today the kids made "magic in a cup" as they called it! This was a really fun experiment. I had seen it many times online, and decided the twins were finally old enough to do it. Big Kid thought it was cool, but the twins were just amazed and were very disappointed when we ran out of spoons!
I put a drop of food coloring on each spoon, then covered the spoons in baking soda (sodium bicarbonate).
Then I partially filled little cups with water (plain H2O) or vinegar (acetic acid) and moved the cups around so we couldn't tell which was vinegar and which was water. They don't need much liquid in them, really! The boys got to pick a spoon and mix it into the liquid in the cup. Some were "magic" and others weren't :) This one here was definitely magic! The cups with water turned colors because of the food coloring, but the cups with vinegar made colored foam and erupted out of the cups.
It's a double replacement reaction. The acetic acid reacts with the sodium bicarbonate to form carbonic acid, which is very unstable. The carbonic acid immediately comes apart into carbon dioxide and water, a decomposition reaction. The bubbles are the carbon dioxide being released! CO2 is heavier than the air so it pours out of the cup down the sides. You're left with a colorful solution of sodium acetate and water! It was fun to mix the colors when we were done too, as my four year olds figured out :)