Activities | Chemistry and Biotechnology

A rainbow worthy of a scientist

Introduction:

Chemical substances are classified according to their properties. One possible classification is to divide them into acids or bases.  Here we use purple cabbage to find out if it is an acid or a base.

Preparation:

Boil half purple cabbage cut into small pieces in a little water and leave to cool.

Remove the cabbage and collect the dark liquid that is left in the pan.

In different test tubes put a few tablespoons water, lemon juice, colourless fizzy drink and dish wash detergent.

In each container add a few drops of water from the purple cabbage until, like magic, you get a different colour.

Why is this so?

The purple cabbage, like beetroot and red plums, has pigments that change colour with acidity. So, it turns acid solutions (like the one containing lemon or vinegar) pink and basic solutions (like the one containing dish wash detergent or soap) green or blue. Substances that are neither acidic nor basic are called neutral.