Colourful Chemicals

Colourful Chemicals

Use cabbage water to change kitchen chemicals different colours.

Suitable for kids aged 4+ with parental supervision

CAUTION The cabbage water must strictly be prepared by an adult as it involves the use of boiling water.

You Need:
  • Small amount of red cabbage
  • Pot of boiling water (to be handled only by an adult)
  • Large container to drain cabbage water
  • Baking soda
  • Citric acid
  • Plastic spoons
  • Small plastic containers (labelled citric acid, baking soda, cabbage water)
What to do:
  1. Important: have an adult chop half a red cabbage and bring it to boil in water on the stove. Stir well and leave it to soak for about 15 minutes.
  2. Once cool, strain the now purple cabbage water and discard the pieces (you do not need them).
  3. Fill a plastic cup with the cooled cabbage water for use in the rest of the experiment. The remaining cabbage water can be frozen for future use.
  4. Cover the bottom of the three labelled dishes with cabbage water.
  5. Now for the fun. Add one teaspoon of citric acid to the cabbage water in the ‘citric acid’ labelled dish and give it a stir. What happens?
  6. Add one teaspoon of baking soda to the cabbage water in the dish labelled ‘baking soda’ and give it a stir. What happens?
  7. Tip the citric acid and cabbage solution into the baking soda and cabbage solution. What happens? Why?
  8. As a further experiment, test other substances with cabbage water and see what colour it turns. For a start you could test the vinegar and detergent. Other chemicals you might like to try could be: lemon juice, orange juice, toothpaste and milk.

Why is it so?

Red cabbage contains a coloured chemical which acts as an indicator. The purple dye in the cabbage water changes colour when mixed with an acid or a base. It turns a red/pink colour when mixed with an acid, and a green/blue colour when mixed with a base. Citric acid is the acid in this experiment, and when mixed with cabbage water turns a pink colour. Baking soda is the base and turns green when mixed with cabbage water. Is vinegar an acid or a base?

When citric acid is mixed with baking soda, the acid and base cancel each other out making a neutral purple solution. The bubbles are a result of a chemical reaction between citric acid and baking soda making carbon dioxide gas.

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