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Red Cabbage Indicator

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A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

Extracting an indicator from red cabbage
This activity involves blending the chopped-up red cabbage leaves in water to get a solution of extracted dye. The extract is then tested to see the colour change when it is added to acidic and alkaline solutions.
The basic experiment can be extended to extract dyes from other vegetables (beetroot, for instance).

1. Cut up the red cabbage into small pieces and blend them using a blender.
2. Put the juice into a beaker and filter the mixture.
3. Pour the solution into several transparent cups.
4. Test the colour change by adding drops of acid.
5. Test the colour change by adding drops of alkali.
6. Test the colour change for the following substances and record the results and conclusions for each:
Baking soda, Lemon juice, Vinegar, Drain Cleaner, Sprite (carbonated drink), Ammonia, Salt, Bleach
Find out how natural pH indicators vary between beets and cabbage
1. What is it in acidic and alkaline solutions that the indicator is responding to?

  • Show Solutions
    1. The indicator is responding to the concentration of H+ and OH- ions in the solution. An acidic solution has an excess of H+ ions and an alkaline solution has an excess of OH- ions. A strong acid has more H+ ions than a weak acid. A strong alkali has more OH- ions than a weak alkali.

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