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Mystery #4Tier 2acids / chemistry

Why does red cabbage water change colour like magic?

Boil red cabbage and you get a purple water. Add a squeeze of lemon and it flushes pink; add some soap and it turns blue-green. No dyes, no tricks. What makes one purple liquid flip through a rainbow?

Red cabbage indicator showing a range of colours across the pH scale
Photo: Yves.brenner · CC BY-SA 3.0 · via Wikimedia Commons

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