Red cabbage can be used as a simple acid/alkali (pH) indicator. This provides a great way of visually telling the difference between acids and alkalis.
Take a leaf from a red cabbage and chop into small pieces. Soak in a small amount (approx. 200ml) of tap water (distilled water can be used if available), then strain to remove the chopped cabbage, saving the liquid.
If facilities exist the water and cabbage mixture can be heated and brought to the boil for a few minutes. This provides a much stronger colour and visual effect.
Then some of the cabbage water can be added to various acids/alkalis. Acids should turn red, water/neutral should turn blue and alkalis should turn green. For the strong colours seen in the photos boiled cabbage water was used in laboratory acids/alkalis which were initially colourless. However, it should work perfectly well with household acids such as lemon juice or white vingear and alkalis such as kitchen/bathroom cleaner.
Red cabbage water indicator placed in an initially colourless acid (turns red), in water (turns blue) and placed in an initially colourless alkai (turns green). Red cabbage indicator liquid is shown on right.
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