The Acidic Environment > 1. Indicators >
Perform a first-hand investigation to prepare and test a natural indicator
- To prepare a natural indictor:
- Select a suitable coloured plant material, such as purple cabbage.
- Extract the colour from the plant material by either:
- Boiling it in water.
- Crushing it with water or alcohol using a mortar and pestle.
- Decant the solution from the solid.
- To test a natural indicator:
- Dip the ends of two strips of filter paper into the indicator and allow to dry.
- Using an eyedropper, apply a drop of strong acid to one strip and a drop of strong base to the other strip.
- Record any changes in colour.
- Add additional drops of acid and base to the strips until no further changes in colour are observed.
- If an indicator is prepared from purple cabbage, the following colours should be observed:
- Initial/Neutral colour: Purple
- Colour when exposed to strong acid: Pink, then Red
- Colour when exposed to strong base: Blue-Green, then Yellow
Purple cabbage