When I was in school, I remember using litmus paper to test the PH of different materials. I don’t have litmus paper, but I learned this great way to make your own indicator out of red cabbage (thanks to www.funsci.com).
Acid – a chemical that will donate a proton (also called a hydrogen ion)
Base – a chemical that will accept a proton
How to make the indicator:
Put a quarter of a red cabbage in a blender with about 2 cups of water and blend it. Chop it up before you put it in the blender. I chopped mine into about 5 or 6 chunks, but it would have gone more smoothly if I had chopped it up more.
Add more water if it is too thick. The amount of water is not critical. Just make it thin enough that you can strain it through a fine strainer or paper towel. Throw out the solids and you have a nice purple liquid.
Use a pipette or a straw to place some of the cabbage juice onto a white surface (like a plate). Then, with another straw or pipette, place some of the substance that you want to test. Mix them a little if needed.
If it turns red, it is an acid.
If it turns blue, it is a base.
Some reactions were mild, indicating a weak acid or base. Some were very dramatic, indicating a stronger acid or base.
We even had some substances that were so basic that they turned green.
The dishwasher soap turned the indicator green! I added more of the cabbage juice and did not mix it. If you look closely, you can see that the area right around the cabbage juice is blue (indicating a base) and then as it is mixed with more of the dishwasher soap, it is green (showing it to be a strong base).
If there is no color change, it is neutral. (No pictures for this – because it is boring)
Sometimes we could get the indicator and the substance we were checking to mix only on part of the plate. This gave a nice comparison.
Here is a group picture so you can see the variety of colors that you can get.
For some substances like dishwasher soap and brown sugar we needed to dissolve some in water and then add that solution to the cabbage juice. (use as little water as possible).
Make sure that you use new materials (straws, pipettes, plates) each time, or clean them, so that there is no contamination of the substances you are testing.
What should you test? Anything you want. Check out the pictures for some ideas. My kids also came up with some other ideas after we cleaned up: toothpaste, hairspray, mouthwash, … (I think we will have to do this one again).