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Experiment

The pH Colour-Change Lab

Boil red cabbage into a purple liquid that turns pink or blue-green depending on what's mixed in.

Ages 7–1025–40 min1–3 kids

An adult boils chopped red cabbage to make a purple liquid, then the child adds small amounts of vinegar, baking soda solution, and lemon juice to separate cups of it, watching the colour shift toward pink or blue-green depending on what's added. Test a few more household liquids to predict and check which way each one shifts the colour.

What you need

  • red cabbage (adult-prepared)
  • small clear cups
  • vinegar
  • baking soda dissolved in water
  • lemon juice

How to do it

  1. 1An adult boils chopped red cabbage in water for about ten minutes, then cools and strains the purple liquid.
  2. 2Pour the purple liquid into several small clear cups.
  3. 3Add a small amount of vinegar to one cup, baking soda solution to another, and lemon juice to a third, watching each colour shift.
  4. 4Predict and test a few more safe household liquids, sorting results into 'turned pink' and 'turned blue-green.'

Variations

  • If boiling cabbage feels like too much prep: bottled purple cabbage juice, if available, works the same way straight from the bottle.
  • How it ends: a final results chart -- which liquids were acids, which were bases -- gives the lab a clear, satisfying wrap-up.

💡 Parent tip

The colour-changing liquid stains, so work on a tray or outside and use cups that don't need to stay pristine.

What your child develops

  • Acid-base chemistry — a real pH indicator reaction, genuinely used in school science years later
  • Prediction and testing — guessing the colour shift before checking builds hypothesis-testing habits
  • Sorting and classification — grouping results into two clear categories reinforces logical thinking

Safety notes

  • The boiling step must be done by an adult. Avoid tasting any of the test liquids or mixtures.

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