How to Make a pH Indicator from Red Cabbage

Learn how to create a natural pH indicator using red cabbage that changes colors when mixed with acids and bases.

1. What You'll Need. Gather these materials: 3-4 leaves of red or purple cabbage, 2 cups of water, a medium pot, a strainer, clear containers or glasses, and household items to test like lemon juice, baking soda mixed with water, vinegar, soap mixed with water, and antacid tablets dissolved in water. You'll also want a notebook to record your observations.
2. Making the Cabbage Indicator. Tear the cabbage leaves into small pieces and place them in the pot with 2 cups of water. Ask an adult to help you boil the water for 10-15 minutes until the water turns deep purple. Remove from heat and let it cool completely. Strain out the cabbage pieces, saving the purple liquid - this is your pH indicator. The liquid should be a rich purple or blue color.
3. Testing Different Substances. Pour a small amount of your cabbage indicator into several clear containers. Add a few drops of your test substances one at a time to different containers and watch what happens. Acids like lemon juice and vinegar will turn the indicator pink or red. Bases like baking soda solution and soapy water will turn it green or blue. Neutral substances won't change the color much.
4. Recording Your Results. Write down what color each substance makes and try to put them in order from most acidic (reddest) to most basic (greenest or bluest). This helps kids understand the pH scale and see patterns in how different household items behave chemically.
5. Understanding What's Happening. Explain to your child that everything around us is either acidic, neutral, or basic. The cabbage indicator works because special molecules in the cabbage change shape when they encounter acids or bases, which changes the color we see. This is the same principle used in pH strips and other scientific indicators.