|#2: Acid and Base Explorations|
If you take half a head of purple cabbage and simmer it a few minutes in enough water to fully cover it, you can get a two-liter bottle of acid/base indicator liquid. You can use this liquid directly in clear cups or you can soak absorbent paper in it and then let it dry to make test strips which can be dipped in test liquids. The absorbent paper can be paper towels or coffee filters.Because this provides so much indicator liquid, you can feel free to do lots of things with it without running out. I like to begin with letting my younger boys experiment on their own with it. I give them a container of water with baking soda mixed in, a small bottle of vinegar and a container of cabbage indicator. I tell them that they can do whatever experimenting they want with it except they cannot eat any of these materials. I know they are all non-toxic, but they are not particular good just to drink and it sets a good precedent for the chemicals they will use later on in chemistry.
Then we used our indicator to determine whether the liquid was an acid or a base. They could easily see that all the ingredients that were sour also turned pink, indicating that they were acids.The liquids that were slippery when you rubbed them between your fingers turned green and were bases.I encouraged them to experiment with the liquids and indicator, pouring the contents of one cup into another and they discovered that after much experimentation that all of the cups turned a purple, and indicated that they had neutralized and were not either base nor acid.
|And so they mixed and poured...|
|and exclaimed over the color changes...|
|It captivated their attention for quite some time.|
They were eager to find out what colors meant what about the pH of the liquids because they had already experimented until they were satisfied. They were ready to find out what it all meant now.
So we tested some unknown liquids and put them in the correct categories.