Kitchen chemistry for 7 to 12 year olds: the red cabbage test
W4C Science · Chemistry · 4 min read · Evidence: established science; activity is classroom practice
A red cabbage, some vinegar and baking soda are enough to show children how chemists tell acids from bases. It takes one hour, costs almost nothing, and children remember it.
Red cabbage contains a natural dye that changes colour depending on how acidic or basic a liquid is. In an acid such as vinegar or lemon juice it turns pink. In a base such as baking soda dissolved in water it turns green or blue. In plain water it stays purple. That makes a cabbage a free "indicator", the same idea as the test strips used in laboratories.
How to make the indicator
An adult chops a quarter of a red cabbage, covers it with just-boiled water, leaves it for 15 minutes, strains it and lets it cool. The purple liquid keeps for two days in the fridge. Children never handle the hot water.
The investigation
Pour the same amount of indicator into five clear cups.
Add ten drops of a different liquid to each: vinegar, lemon juice, water, baking soda in water, washing-up liquid in water.
Record the colours, then line the cups up from pinkest to greenest.
Ask a fair-test question: does adding more drops change the colour more? Keep the indicator the same and change only the number of drops.
The most valuable part is the prediction. Before each liquid goes in, ask children what they expect and why. A wrong prediction is useful: it shows exactly what they thought before.
Keep it safe
Even kitchen materials become lab materials. Children wear goggles, taste nothing, and wash their hands afterwards. The US National Science Teaching Association recommends splash goggles whenever chemicals are used with primary pupils, and handwashing after every chemistry activity. Use only kitchen-safe substances; never bleach or cleaning products.
Try this tomorrow. Ask each child to bring one safe liquid from home in a labelled bottle (tea, fizzy water, juice). Predict its colour, then test it. Add it to a class colour chart from pink to green.
Related resource: W4C-120 Young Scientists Lab includes this session with a printable investigation sheet, plus 19 more investigations in chemistry, biology, earth science, astronomy and environmental science. Coming soon to EduStore; subscribe to the newsletter to hear when it opens.
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