Question to investigate
How can you use a red cabbage to test and classify substances?
Chemistry concepts
- Acids and bases are classes of materials that have different properties.
- Acid-base indicators change color depending on whether they are in acids or bases.
- Red cabbage leaves contain a substance called anthocyanin that changes color depending on whether mixed with an acid or a base.
Activity logistics
- Ages: As written, this activity is suited for ages 8–12.
- Time: 45 minutes–1 hour
Be safe
- Do not eat or drink any of the materials used in this activity.
- Work with an adult.
- Read and follow all directions for the activity.
- Read all warning labels.
- Wear Personal Protective Equipment (PPE), such as goggles, safety glasses, or gloves.
- Tie back long hair, roll up sleeves, and secure loose clothing.
- Be sure to clean up and dispose of materials properly when you are finished with an activity.
- Wash your hands well before and after the activity.
Disposal: Dispose of all solid waste in the trash. The liquids can be safely disposed of down the drain with plenty of water.
What you’ll need
- Red cabbage
- Household items to test, like:
- Fruit juice, for example: lemon, lime, orange, apple
- Soda pop (light-colored sodas work best)
- Vinegar
- Milk
- Yogurt
- Liquid cleaning products (don’t use bleach)
- Solutions made by dissolving a solid such as baking soda, detergent, or baking powder in water
- Bowl
- Water
- Zip-closing plastic bag
- Dropper or straw
- Several small cups (one for each test)
- Small bowl or cup
- Measuring cups
- Measuring spoons
* You can use a straw as a dropper. First, dip the straw into the liquid. Place a finger over the top of the straw to make a seal. When you remove the straw from the liquid, the liquid will remain inside the straw. When you are ready to release the liquid, remove your finger from the top of the straw.
What did you observe?
Download this worksheet to record your observations.
How does it work?
Chemists classify substances as acids or bases. Lemon juice and vinegar are both examples of acids. On the other end of the spectrum are bases. An example of a base is baking soda, which you might have used in the kitchen to make cookies and cakes. Many soaps are bases. Some substances are neutral, meaning they are neither an acid nor a base, like water.
How can you tell if something is an acid or a base? Acids and bases can change the color of substances called acid-base indicators.
Red cabbage contains a chemical called anthocyanin. This pigment is a natural acid-base indicator. It is blue in neutral substances, like plain water. When an acid like lemon juice gets in the water, a reaction makes the indicator molecule change shape and it looks pink. When instead a base gets in the water, a different reaction happens that changes the indicator molecule and it looks green.
This activity is adapted from an activity that originally appeared in the Celebrating Chemistry issue for Chemists Celebrate Earth Day 2010.
