2003-06-10
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.
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.
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.
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