Believe it or not, a very ordinary ingredient (red cabbage!) can actually serve as a litmus indicator, just like the fancy litmus paper in a school chemistry class. Today, Travis made a batch of this purple indicator solution and we tested a few liquids around the house.
To make the indicator, rip a head of red cabbage into shreds then cover with hot water in a bowl. Let stand for about 30 minutes. Strain through a sieve over a second bowl or measuring cup and you’ll have a bright purple liquid!
We started out with two separate solutions: the first was about a teaspoon of citric acid in 1/4 cup water, and the second was a teaspoon of baking soda in 1/4 cup water. Imagine Travis’s surprise when an eye dropper of the purple indicator solution turned the citric acid pink and the baking soda blue!
He immediately wanted to test other liquids. We tried water next, and he discovered that the indicator stayed exactly the same purple. I pointed out to him why this is so on the pH scale, with water “neutral” in the middle.
Vinegar turned his indicator very pink and soy milk turned it bluish, although this was a bit hard to see.
As a final test, he wanted to try apple juice, which turned a deep pinkish orange as well.
Note: We later learned that you can repeat this experiment with other fruits and vegetables, including onion, blueberries, cherries, and beets.
Unfortunately, despite soaking these four foods in hot water just like the cabbage, we weren’t able to change the color of vinegar. Your kids can have fun testing this out, and please share any fun findings in the comments!