Colourful Acid / Alkali Experiment

This is an interesting and colourful acid/alkali test using boiled red cabbage water as a simple indicator.

If you don’t have any red cabbage, black tea also makes a good though slightly less colourful) indicator. Indicator paper may also be used and will give a better indication of substances that are only weakly acid or alkali.

Instructions:

1. Boil a couple of red cabbage leaves in a saucepan of water and allow to cool.
2. Remove the leaves and pour the contents into a number of glasses.
3. Add the substances you wish to test to the glasses (leaving one as your ‘neutral’) You can see what we used in the picture below – rollover to see whether they were acid or alkali.

4. As you can see above the red cabbage water turned bright pink if the substance was very acidic like lemon and dark greenish if alkali like baking soda.

Contemplating the results:

It is interesting when unexpected results crop up. We were expecting the washing-up liquid to be alkali (and even placed the glass where we expected the alkali substances to be). However, it didn’t look at all like the baking soda in the next glass. When we read the ingredients we saw why – one of its main ingredients is citric acid! We later tested Fairy Liquid (not shown below) and this was alkali.

The colouring of some substances seemed to obscure the results – balsamic vinegar’s very brown colour meant that although it’s very acidic it doesn’t produce the same bright pink that the lemon did. Maybe a less colourful wine or apple vinegar might work better.