Red Cabbage pH Indicator

An adult should handle the boiling water used to extract the cabbage juice, and supervise use of the household acids/bases being tested (e.g. lemon juice, vinegar, baking soda solution).

Disposal: All liquids can be safely poured down a sink drain with running water.

Do not start this experiment until an adult who has read the supervision notes above is present.

Materials

• Red cabbage, chopped
• Boiling water (adult handles this step)
• A sieve or strainer
• Several clear cups
• Household liquids to test (lemon juice, vinegar, water, baking soda dissolved in water, soap solution)

Steps

1. An adult pours boiling water over the chopped red cabbage in a heatproof bowl and lets it sit for about 10 minutes; the water will turn deep purple.
2. Strain out the cabbage pieces, keeping the purple liquid — this is the pH indicator.
3. Pour a small amount of the purple indicator into several clear cups.
4. Add a different household liquid to each cup and observe the colour change: reds/pinks indicate acidic, purple stays roughly neutral, blues/greens indicate basic/alkaline.
5. Record which liquids caused which colour, from most acidic (reddest) to most alkaline (greenest/yellowest).