Cabbage Indicator

Yesterday while I was out shopping I saw half a red cabbage on sale for about a dollar. Immediately I thought about an experiment I did years ago as a kid, where I used the juice as a substitute for universal indicator, so I grabbed it for use later.

boiling up the cabbage

This morning after cooking pancakes for breakfast I chopped and boiled the cabbage to extract its pigment. The plant dye is commonly referred to as a Flavinoid. More specifically it is an Anthocyanin who's absorption wavelength changes with pH.

indicator colours at different pH

The purple tube is the neutral colour, around pH 7. The green is the result of adding a tiny drop of bleach. The yellow is even more alkaline, I put a small pellet of caustic soda (sodium hydroxide) in the tube. The pink is from a few drops of vinegar. I don't have a stronger acid in the house, a few drops of hydrochloric acid should send it towards deep red.

If you have access to buffers of various pH or a digital pH meter you can calibrate the indicator colours accurately and use them for titration.