Activity: Acid or base?
Traditionally an acid is something that tastes sour, like a lemon, and a base is something that tastes bitter or is slippery, like soap. But taste and touch are not good senses to use in chemistry because many substances are poisonous or can hurt our skin.
There is a way that we can use our sense of sight to tell acids and bases apart. We can use special dyes, called indicators, which change colour if something is an acid or a base.
You will need:
- Sliced red cabbage (get an adult to help you slice it up)
- Hot water
- 2 Jugs
- Strainer
What to do:
Put the cut cabbage into a jug, and pour the hot water over the cabbage. Leave the cabbage and water for at least 10 minutes.
Using the strainer to catch the cabbage, pour the coloured water into the other jug (you can put the cabbage in your compost or worm farm). The coloured water is now ready to use as an indicator.
To test if a substance is an acid or a base, pour some of the mystery substance into a small glass. Add your cabbage indicator and look for a colour change.
Some ideas for things to test are:
- Vinegar
- Baking Soda
- Toothpaste
- Ammonia
What do the colours mean?
- Red: Strong Acid
- Yellow: Moderate Acid
- Green: Weak Acid–Neutral
- Blue: Neutral–Weak Base
- Purple: Moderate Base
- Violet: Strong Base
You can use this indicator to test your grey water before it goes on the garden. It is better for the plants in your garden if it stays a green or blue colour (not a strong acid and not a strong base).
