Colorful Cabbage

Did you know you can make a pH indicator using red cabbage? Let’s cook up some science!

What you will need:

  • A small head of red cabbage
  • A large cooking pot
  • A strainer
  • A variety of liquid acids and bases (vinegar, lemon juice, detergents, clear soft drinks, baking soda diluted in water, window cleaner, etc.)
  • Small cups (paper, plastic or glass)

Here’s what to do:

  1. Cut the red cabbage into small pieces and place them in a big pot.
  2. Fill the pot with enough water to cover the cabbage and boil for twenty minutes, or until the water turns purple or blue.
  3. Wait for the liquid to cool, then strain out the cabbage and pour a couple of tablespoons of this liquid, which will be your pH indicator, into a number of small cups.
  4. Add a different acidic or basic liquid to each of the cups until the color changes.

Take it further:

  • What color changes do you notice?
  • Do some liquids generate similar color changes?
  • Do you notice anything else happening to these liquids, other than color changes?

What’s going on?

What causes the color changes? Pigments called anthocyanins are present in red cabbage. These pigments change color depending on the pH of their environment. In acidic solutions, the pigments turn red/pink, in neutral solutions they stay blue/purple, and in basic solutions they turn yellow/green. You can try to find other pH indicators by testing various pink/purple fruits, fruit juices and flower petals. You can also visit www.howstuffworks.com and type in “pH” and “anthocyanins” to find out more.

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