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Sari on Science: Making cabbage chemistry rainbows

What’s better than cabbage and rainbows in March? Boiled cabbage may be an acquired taste (and smell!), but you can try your luck and some science magic to get your kids to enjoy this red cabbage activity. It won’t yield a pot of gold, but you will get to create a rainbow of kitchen chemistry and fun!

Supplies:

  • 1 head red cabbage
  • Safety glasses
  • 6 cups boiling water
  • Blender
  • Strainer
  • Large bowl or pitcher
  • Measuring cups
  • Measuring spoons
  • Large sealable container to store cabbage juice (clean 2L bottle, milk carton, etc.)
  • 5 clear drinking glasses
  • Lemon juice (fresh or bottled)
  • White Vinegar
  • Baking Soda
  • Laundry detergent
  • Spoons or sticks for mixing
  • Optional: Milk, antacid tablets, ammonia, soda/soft drinks, other fruit juice, sports drinks, etc.

Directions:

  1. Using an adult’s help and wearing safety glasses, bring 6 cups of water to a boil.
  2. While the water is heating, set up the blender. Rip up a few cabbage leaves and place them in the blender.
  3. Very slowly add 2 cups of boiling water to the blender. Blend until the leaves are a fine pulp. Add more water if needed. (NOTE: Use caution. Hot mixture could pop blender lid off.)
  4. Pour the resulting cabbage juice into the bowl/pitcher, using a strainer to remove any small solid pieces/pulp. Discard the cabbage pulp (or add it to your compost pile).
  5. Repeat until you’ve used all the water. One head of cabbage can make more than a gallon of juice, so it’s up to you if you want to use all of it.
  6. Allow the cabbage juice to cool. Store in a sealed container in the refrigerator if not using immediately.
  7. Fill all 5 glasses at least ½ full with cabbage juice. Make observations: what does it look like?
  8. Add 1 teaspoon of lemon juice to one glass of cabbage juice.  What do you observe?
  9. Add 1 teaspoon of baking soda to a separate glass of cabbage juice. What do you observe?
  10. Continue this for each of the materials you want to test (vinegar, laundry detergent, milk, etc.), adding only that material to the cabbage juice. Leave one glass of cabbage juice with nothing in it as your control.

What’s happening?

What did you observe? What color was your cabbage juice to begin with? Red cabbage contains a pigment called anthocyanin, which causes it to appear purple in color. This chemical changes color depending on the pH of its environment, so we call it a pH indicator.

When we add something acidic, like lemon juice, to the neutral purple, it will change color to a lighter and brighter pink or red. When we add something more basic or alkaline, like baking soda or ammonia, it will turn blue, green or even yellow! Try testing some other materials in your kitchen, like milk or soft drinks, and make predictions about what color you think they will turn. What did you observe?

When you’re done testing, try organizing your colors into most acidic to most basic and snap a rainbow picture. Did you know: A popular tea made from the purple Butterfly Pea flowers also has these same color-changing properties since it contains anthocyanin pigments. What other foods do think might have the same properties?

Love hands-on science? Find more activities at our Camp Innovation during Spring Break (March 9-13 and 16-20) at Arizona Science Center. Find more information at azscience.org

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Kara G. Morrison
Kara G. Morrison
Kara G. Morrison is the editor of Raising Arizona Kids and the mother of Sofia (8).

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