Acids, Bases and Cabbage Water
- Chemistry
- Ages 8–11 · Grades 3–5
- Hands-on experiment
What you’ll find out
- Acids and bases are two opposite families of substance.
- An indicator changes colour to show which one it is in.
- Mixing an acid and a base cancels them out.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Two opposite families
Bite a lemon and it is sour. Vinegar is sour, and so are oranges. All of these are acids. Now feel a bar of soap: it is slippery, and baking soda belongs to the same family. These are bases. Acids and bases are two opposite groups of substance, and plain water sits in the middle, belonging to neither. You must never taste or touch something to work out which one it is — strong acids and strong bases can both burn skin badly. There is a much safer way to tell.
Cabbage water tells you which
Boil a few red cabbage leaves and the water turns deep purple. That purple water is a test you can use. Add a little lemon juice and it turns pink. Add baking soda instead and it turns green. Add plain water and it stays exactly as purple as it was. A substance that changes colour to tell you what it is in is called an indicator. Now try adding both the lemon juice and the baking soda to the same glass: the colour comes back towards the middle, because the acid and the base have cancelled each other out.
Curriculum links: NGSS 5-PS1-3 · NGSS 5-PS1-4