One of the things we did for our mad science party was cabbage juice pH testing. I heard about it from a friend and found that it was sooo fun. This is a great science experiment to do for a group. It is done with common stuff that is most likely sitting around your house, so it's pretty cheap as well. Win-win.
Red cabbage contains a pigment molecule called flavin. When a solution is neutral, the color is a nice purple, while acidic solutions make it a red color and basic solutions make it a greenish-yellow color.
First, you start off with a head of red cabbage. Chop it up. The pieces don't need to be too small, but you want them to be able to loosely float in the water to cook.
Put the cabbage in a large stockpot and cover with water.
Boil it on the stove for about 10 minutes or so, until the water starts to look dark and the cabbage looks pretty wilted. The important part is that you want to have the color, which contains the flavin, to leech into the water.
Strain out the cabbage. The resulting water will be a beautiful dark purple color.
As the solution cools, gather up your reagents. A reagent is just something that you mix together to make a chemical reaction. I just used things that were found around my house. The vinegar, orange juice, club soda and hydrogen peroxide are acids, you will see them turn the solution to varying shades of red. The antacids, cream of tartar, baking soda and windex are bases, they will turn the solution to varying shades of green.
Once the cabbage solution is cooled, you are ready to start.
Now, this is the really complicated chemical part.
Ok, just kidding.
You just dump the reagents into the cabbage solution.
Once they are all mixed together, you will get this nice rainbow spectrum based on the acidity of each of the reagents.
This is where you get really excited that things worked so well.
Now, this is one of the fun things you can do for further testing. Mix together the acid and base solutions to see if there are any reactions. Since one solution contains vinegar and another contains baking soda, you could come up with fun stuff like this.
*Note* Be very careful. The acids and bases I used are pretty weak and will not react harshly. If you use strong acids and bases, you could get hurt. Just saying.
As you mix the acids and bases together, they will neutralize and turn closer back to the neutral purple solution, like the one on the left below.
Another fun thing is that the hydrogen peroxide will eventually turn the solution clear, since it has bleaching properties.
What can I say? I am a complete nerd.