Materials
- Red cabbage
- Hot water
- Blender or bowl and spoon
- Strainer or coffee filter
- Clear cups or containers
- Various household liquids (e.g., vinegar, lemon juice, baking soda solution, soap, water)
- Optional: Ice cube tray for indicator storage
Procedure
- Chop red cabbage into small pieces and place in a blender or bowl.
- Add hot water and blend or mash until the water turns purple.
- Strain the mixture to collect the purple cabbage juice.
- Pour the juice into clear containers.
- Add different household liquids to each container and observe color changes.
- Optional: Freeze indicator in an ice cube tray to use later!
Choose Your Learning Level
Elementary
Red cabbage makes special purple juice that can change colors when you mix it with things like lemon juice or soap. It's like cabbage magic! Acids turn it pink, and bases turn it green or blue.
Discussion Questions
- What color did you see when you added vinegar?
- Which liquid made the biggest color change?
- Can you make a rainbow using cabbage juice?
Middle School
Red cabbage contains a pigment called anthocyanin, which changes color depending on how acidic or basic a liquid is. This makes it a natural pH indicator. Acids turn it reddish, while bases turn it greenish or blue.
Discussion Questions
- What colors did you see for each substance?
- Which substances are acids, and which are bases?
- What other foods might make pH indicators?
High School
Anthocyanins in red cabbage are pH-sensitive molecules. In acidic environments (pH < 7), they appear red; at neutral pH, purple; and in basic environments (pH > 7), they shift to green or yellow. This experiment models pH indicators used in titrations and chemical analysis.
Discussion Questions
- How does the molecular structure of anthocyanin affect its color under different pH conditions?
- What advantages do natural indicators have over synthetic ones?
- How would you create a pH scale using cabbage juice?