Red Cabbage Rainbow pH Indicator

Boiled red cabbage produces a purple solution containing anthocyanin, a natural pigment that changes color when exposed to acids or bases. Students can use this homemade pH indicator to test household substances and create a rainbow of colors across the pH scale.

1. Chop red cabbage and boil it in water until the liquid turns deep purple.
2. Strain and cool the liquid to collect the cabbage extract, which serves as the indicator solution.
3. Prepare a series of test tubes with water.
4. Add small amounts of acidic and basic solutions to adjust the pH across a range of values.
5. Place a few drops of cabbage indicator into each test tube and observe the resulting color changes.
6. Compare colors to approximate pH values, creating a visual rainbow of acidity and alkalinity.
7. Test common household substances such as vinegar, lemon juice, baking soda solution, dish soap, antacid solution, and bleach by adding the indicator and recording the color change.

Red Cabbage Rainbows - Royal Society of Chemistry:

pH Rainbow Tube - Kitchen Chemistry Experiment - Anne Helmenstine:

📄 Students Turn Kitchen Science into a Red Cabbage Rainbow - MICDS: https://www.micds.org/news/article/students-turn-kitchen-science-into-a-red-cabbage-rainbow/

• Try other natural indicators like beet juice, turmeric, or blueberry extract.
• Use cabbage indicator on pH paper to compare precision with liquid testing.
• Test beverages (soda, coffee, tea) for acidity levels.
• Create a full-scale pH color chart by matching indicator colors to known pH solutions.

• Use caution when boiling cabbage; handle hot liquids carefully.
• Wear goggles and gloves when testing strong acids or bases like bleach.
• Dispose of chemicals safely and according to school or lab guidelines.
• Clean up spills promptly to avoid staining from the cabbage solution.

• Why does red cabbage change color with different pH levels? (The anthocyanin pigment changes molecular structure in response to hydrogen ion concentration.)
• What color does cabbage juice show at neutral pH? (It appears bluish-purple around pH 7.)
• Why do different household substances show different colors with the indicator? (They contain varying levels of acidity or alkalinity, altering the pH.)
• How does this compare to a commercial pH test strip? (Cabbage gives a broad color range but is less precise than standardized pH paper.)