Red Cabbage Test

Some substances we use in the kitchen are classed as either an acid or a base. Acids have a low pH and bases (alkaline) have a high pH. The pH scale goes from 0-14 and purified water (a neutral) is rated 7. Scientists use an indicator to detect the acidity of a substance as the indicator changes colour when it comes into contact with an acid or a base. 

In this experiment we will be using red cabbage water as an indicator. When the red cabbage water comes into contact with an acid it will change colour to red. When it comes into contact with something basic it will turn green! How cool! Now we can explore different kitchen items to discover their acidity. 

You will need: 

  • Red Cabbage

  • Pot of hot water

  • Items to test (vinegar, laundry detergent)

  • Sieve

  • Funnel

  • Small clear cups

  1. First roughly chop a quarter of a red cabbage and pour into a pot. ​

  2. Next add enough boiling water to completely cover. Return this to the boil and then simmer for 10 minutes. 

  3. Strain the mixture through a sieve so you have separated the liquid and the cabbage. 

  4. Use the funnel to pour the liquid into some small test cups.

  5. Add a teaspoon of each item to test and stir into the purple cabbage juice. Has the colour changed? What does that tell us about the substance you were testing?

  6. We would suggest you try a cup of vinegar and a cup of laundry detergent first. Then you can try any other items in your kitchen. Try to arrange in a pH scale as we have done in the picture. 

What is happening here? 

Red cabbage contains a special pigment called anthocyanin. This is soluble in water and turns pinky/red when there is a pH less than 7. It turns bluey/green when there is a pH greater than 7. If there is no colour change then it must be a neutral.