|Red Cabbage Indicator
Some dyes act
as indicators - they change colour depending on whether they have
acid or alkali mixed with them.
You Will Need:
- half a red cabbage
- a saucepan
- a sieve
- a bottle and a dropper
- Chop half a red cabbage, place it in a
saucepan and add just enough water to barely cover the
- Bring the water to the boil, and simmer for
about 15 minutes.
- Pour the water through a sieve.
- This purple water is your indicator
Testing the Indicator:
- Place a small amount of indicator dye into
three separate containers.
- Add a few drops of vinegar or lemon juice to
- Add a small amount of bicarbonate of soda (or
baking powder) or cloudy ammonia to another sample.
- Compare each of the mixtures with the third
sample of indicator dye.
The bicarbonate of soda or ammonia
(alkalis) should have turned the cabbabge water a pale
greeny-blue. The vinegar or lemon juice (acids) should have
turned the cabbage water a reddish colour.
The red cabbage dye is behaving as an
indicator, a chemical substance which changes colour,
depending on the acidity, or alkalinity of its environment.
Parker, S. Simple
Chemistry (London: Kingfisher, 1990).