Indicators in Chemistry

Year 8 have been learning about acids and alkalis. Most acid and alkalis are colourless, so as part of this unit they have looked at ways of identifying the pH of an unknown solution.

Initially, we used the classic universal indicator. This is a mixture of chemicals that gives a wide range of colours, from reds and yellows for acids, to deep purple for strong alkali. However, this is not the only indicator that can be used. Before breaking up for half-term we made red cabbage indicator, which is a simple process. When the students returned to school they used the indicator to test for acids and alkalis. Despite the quite intense boiled cabbage smell, the indicator gave us excellent results.

It’s a great bit of practical science that can easily be done at home. Substances such as vinegar, lemonade, bicarbonate of soda, hand soap, bleach and window cleaner will give interesting results.

Method

1. Place some chopped red cabbage in a pan and cover with water.
2. Heat until the water boils.
3. Use a filter or sieve to remove the cabbage leaves.
4. Add the red cabbage solution to various liquids and observe the colour change.

Mr Coogan

Science Department

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