Today, as part of RSO Chemistry, we did one of the really classic homeschool science experiments: making pH indicator out of red cabbage. I’ve heard of lots of people doing it, but I was still rather surprised when it actually worked – and beautifully!
To begin, we measured out four cups of chopped red cabbage, added four cups of boiling distilled water, covered the pan, and let it sit for a few hours. Then we poured it through a strainer to remove the cabbage. We wound up with a lovely purple liquid with an extremely un-lovely smell.
We prepared some homemade litmus paper for our next lesson by soaking coffee filters in the indicator fluid. I confess that I am dubious about whether this will work, but they did dry to a lovely lavender color, so perhaps it will.
Then we dished out indicator into nine clear cups, each labeled with a substance we wanted to test.
The kids took turns mixing our test samples into the indicator and arguing about how to describe the precise color of each sample. Acids are supposed to turn pink or red. Weak bases turn blue and strong bases turn green. We got good strong color changes! The only one that confounded us was dish soap. Soaps and detergents are supposed to be basic, but this one had lemon added, and lemon juice is acidic. The color was more of a muddy brownish-burgundy than anything else, but in some lights it looked grey.
I strongly recommend this experiment. It was very easy, with a big payoff. None of us felt done when we finished the official experiment, so we went around the kitchen grabbing things and testing them until we were out of cups. I’m looking forward to the other acids and bases lessons!