Red Cabbage Indicator

You will need:

Red cabbage (1/4 head)

Water

Vinegar

Baking soda 1tsp

What to do:

• Chop the red cabbage and put into a blender or food processor.
• Add about a cup of water and blend the mixture until the cabbage has been chopped into tiny pieces.
• 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.

• Pour some vinegar into a colourless drinking glass.
• Add 5 millilitres (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.

• Place 1 teaspoon of baking soda in a glass and add 125 millilitres (½ cup) of water.
• Stir the mixture until the baking soda has dissolved.
• Add 1 teaspoon of red cabbage extract to the solution.

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 extract 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 above 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.

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

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.