You will need:

• Red Cabbage (1/4 head)
• Water
• Vinegar (125ml)
• Baking Soda (1 tsp)

What to do:

1. Chop the red cabbage and put into a blender or food processor.
2. Add about 1 cup of water and blend the mixture until the cabbage has been chopped into tiny pieces.
3. Strain the mixture by pouring it through a sieve.

This strained liquid is our red cabbage indicator and we will test it on liquids to see if they are acids or bases.

1. Pour 125ml of vinegar into a clear drinking glass.
2. Add 5ml (1 teaspoon) of red cabbage extract, stir the mixture and write down its colour.

Now let's examine the effect of baking soda on the colour of red cabbage:

1. Place 1 teaspoon of baking soda in a glass and add 125ml of water.
2. Stir the mixture until the baking soda has dissolved.
3. Add 1 teaspoon of red cabbage extract to the solution.
4. What colour does the solution go this time?

How does it work?

Acids are materials that have certain properties in common. Bases (also called alkalis) are other substances with a different set of properties.

The most striking property of both acids and bases is their ability to change the colour of certain vegetable materials. A common vegetable whose colour responds to acids and bases is red cabbage. Red cabbage can indicate whether a substance is an acid (like vinegar) or a base (like baking soda). It can also show how strong an acid or a base a substance is. Chemists use the pH scale to express how acidic (like an acid) or basic (like a base) a substance is. A pH value below 7 means that a substance is acidic, and the smaller the number, the more acidic it is. A pH value about 7 means that a substance is basic, and the larger the number, the more basic it is. Red cabbage extract has different colours at different pH values (see the picture above!).

Test other substances around the house, such as sugar, table salt, shampoo or milk of magnesia.

Don't forget to take some pictures of your red cabbage indicator and send them into us to be in with a chance of winning some great prizes.

The School of Chemistry at NUI Galway advise that adult supervision is needed for all experiments. The portions of materials used in the experiments should not be increased from that described and mixtures prepared should not be ingested. The full text should be read before starting any experiment.

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