Red cabbage as an acid-base indicator

J got the book ‘Kitchen Science Lab for Kids’ by Lee Liz Heinecke for Christmas and today it’s raining so we had a go at one of the experiments. We used red cabbage juice as an acid-base indicator. It worked really well and was lots of fun! So easy to do as well.

First I helped J chop up some cabbage (we had half of one). She’s no stranger to using proper sharp knives as I believe in teaching children to use real tools from an early age. The chopped bits of cabbage went into a pot then covered with water and boiled for 15 minutes. Once the strained juice had cooled we could start the experiments.

The cabbage juice was a dark purple colour which turned blue-green when the base (bi-carb soda) was added and pink when the acid (vinegar) was added. This lead to discussions about pigments (and the wavelengths of visible light), pH, acids and bases, and chemical reactions. J didn’t understand it all but that’s ok. I know she will remember the terminology later on and when we encounter another learning opportunity, we can build on her knowledge.

Lastly was the fun part of adding the vinegar solution to the bi-carb soda solution and watching it foam up! We have some left over cabbage juice so we’re going to add a few other things like milk, salt, and lemon juice to see what happens!

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