Many substances can be classified as either an acid or a base. Lemon juice is a weak acid and like most acids, it tastes sour. A base is the opposite of an acid.
A pH is a way to measure how acidic or base a liquid is. The value ranges from 0 and 7 for an acid and 7 to 14 for a base.
Some strong acids and bases can attack and irritate your skin, so you need to be careful.
This is a simple experiment to find out if a liquid is an acid or a base.
You will need:
- half a red cabbage
- some glasses or clear plastic cups
- a kettle
- two jugs or medium sized bowls
- a couple of teaspoons
- test liquids – we used lemon juice, vinegar, apple cider vinegar, coco-cola, soda water, bi-carb soda, salt, washing detergent, washing-up detergent, liquid soap, rubbing alcohol, and dettol
What to do:
- Cut the cabbage into small pieces and place in the jug / bowl.
- Cover the cabbage with boiling water and let it sit for 10 minutes. You could also use cold water, but you will need to let it sit for 45 minutes.
- Strain the juice into another jug/bowl. This purple cabbage juice is your indicator and it is ready to use.
- Pour equal amounts of the indicator into each of the glasses / plastic cups.
Slowly add your test liquids, one to each of the plastic cups.
Mix in the salt and the bi carb soda with a teaspoon.
The liquids should mix as they are poured in.
What happens to the colour of the indicator / cabbage water?
Our boys completed this worksheet, making their hypothesis before adding the solution to each of the cups.
You can download your free copy below:
Explanation: Red cabbage juice contains chemicals that change colour when mixed with certain other chemicals. When you add an acid to the cabbage juice, it will turn to a different shade of red, but when you add a base to the liquid, it will change to a blue or green colour.
What are some other solutions you could use when doing this experiment?