pH testing with red cabbage
“pH” is the measurement of how acidic or alkaline a substance is. Pure water has a “neutral” pH of 7, meaning it’s neither an acid nor an alkali. A lower pH (1-6) is acidic, while a higher pH (up to 14) is alkaline. You can test the pH of a chemical using a pH meter, or pH indicator.
If you’re looking to get an approximate idea of pH, you can use the humble red cabbage! Keep reading to find out how.
You will need:
A red cabbage, cut into small pieces. How much you need will depend on how much pH indicator you want to make. We used about 1/4 of a cabbage.
A jug or bowl large enough to fit the chopped cabbage.
A kettle or pan to boil water.
A sieve and second jug or bowl
Clear glasses or other containers for testing.
Method:
put the chopped cabbage into the jug or bowl, and pour boiling hot water over the cabbage to cover it
Step 1
Put your chopped cabbage into your jug or bowl and pour hot/ boiling water over the cabbage to cover it. Leave for at least 10 minutes.
Step 2
After 10 minutes, drain the cabbage mixture over your second bowl to catch the now purple liquid.
Step 3
You’ll be left with a purple liquid, pour a small amount of this into a few clear glasses or containers.
Step 4
Try putting a selection of different substances in each glass, to test their pH. You can try this with any liquid or any powder than dissolves in water.
A lower pH will change the colour to pink then red, a higher pH will turn the mixture blue. A very high pH would turn the mixture green then yellow. We used:
Vinegar (acidic)
Lemon juice (acidic)
Nothing added (red cabbage)
Sodium bicarbonate/ baking soda (alkaline)
We tested each mixture with our pH meter, so we’ve labelled each experiment with the measured pH.