Red cabbage turns green on adding to basic solutions. Red cabbage contains a water-soluble pigment called anthocyanin that changes colour when it is mixed with an acid or a base.
How to make a red cabbage indicator
- Three or four big cabbage leaves are peeled off and put in a blender filled one-half full of water. Blend the mixture on high until you have purple cabbage juice.
- Pour the purplish cabbage liquid through a strainer to filter out all the big chunks of cabbage. Keep the liquid for the experiments to follow.
- Take three glasses and pour full of cabbage juice.
- Add a little vinegar to the first glass of cabbage juice. Stir with a spoon and notice the colour change to red, which indicates that vinegar is classified as an acid. All acids will turn red when mixed with cabbage juice.
- Add a teaspoon of washing soda or laundry detergent to the second glass. Notice how the liquid turns green, indicating that this chemical is a base.
- Keep the two glasses of red (acid) and green (base) liquid for future reference. Fill the third glass of purple cabbage juice to show the colour of a neutral solution.