Color Changing Cabbage Juice

Cabbage Juice
Here's what you'll need...
  • 1/2 a red cabbage
  • Water
  • Large microwavable bowl
  • Microwave
  • 3-4 clear cups
  • Various acids and bases to test: vinegar, baking soda, etc.

Making a pH indicator can be fun and surprising. “Cabbage juice,” the purple water that comes from cooking a red cabbage, changes color if it is mixed with an acid or a base. You can make it look like a magic trick, but be sure to explain the science behind it, too!

For a microwave-sized batch of cabbage juice, you only need half a red cabbage, though a whole head can be used for a large pot on the stove. Cut or rip the cabbage in to chunks, so that all the layers can get exposed. Put the chunks into a large, microwave safe bowl (or stove-ready pot) and add water to fill the bowl. Microwave it for about 10 minutes, or until the water gets a good purple color. (The water looks darker after you stir it a bit.)

Separate the cabbage from “juice” using a strainer or by simply pouring it off into a pitcher. If you want, you can get more cabbage juice by refilling the bowl with water and microwaving it repeatedly until the cabbage has lost its color.

Now for the fun part: Add a small amount (1/2 tablespoon) of vinegar to a clear cup. Now pour in some cabbage juice. It changes color! Vinegar is an acid, which means it has a pH below 7. In acids, cabbage juice turns pinks. With an adult’s help, you can also try ammonia. Ammonia is a base (the opposite of an acid) which means it has a pH above 7. In bases, cabbage juice turns green.

With a parent’s permission, test other chemicals around the house, to see if they are acidic, basic, or neutral. (Neutral things, like water, won’t change the color.) Try baking soda, dishwasher powder, and salt. Try soap, lemon juice, or Sprite. What do you think will happen when you mix the baking soda with the vinegar in the cabbage juice?

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