I've read about this experiment in several places and really wanted to try it with my girls. A few days ago, we finally did it and had lots of fun!
What is the Purple Cabbage Experiment?
The basic idea is that purple cabbage juice can be used as a pH indicator. The girls are aware of the pH scale from their weekly testing of the fish tank water, so at least that made the concept easy for them to understand. It's always good to have something in their day to day life to relate things to - it makes things more easily understandable.
How to make purple cabbage pH indicator
The experiment involved first of all extracting the juice from the cabbage. We found 3 different recommendations on how to do this
1. Put cabbage leaves in cold water, bring to the boil and boil for 10 minutes then strain off the juice.
2. Chop cabbage, pour over boiling water and leave to soak for 10 minutes, then strain off the juice.
3. Put chopped cabbage and water into a blender and whizz up! Then strain off the juice.
We decided on what I thought was the simplest method - number 2.
We checked a colour chart we found online as to what colour the purple juice should turn to indicate acid or alkali:
Then we collected some medicine cups and a dropper and chose what substances to test the pH of.
What did we test?
First we tested our own saliva, which should be a healthy alkali.
Both my daughters ones were alkali, mine was neutral. From what I found when researching this online - that would be about right. Kids saliva tends to be more alkaline and adults neutral to acidic.
So success for our first test!
We then went on to test several other things:
Here's the colours after adding the purple cabbage juice indicator..
And some more..
Once again - after adding the purple cabbage juice:
The girls were learning that citrus fruits - like lemon and orange are acidic, and bicarb of soda was a good example of an alkali.
It was good to include the fish tank water in there - and for it to come out as a neutral, just as it had when the girls had tested it with the bought pH test kit earlier that day! Demonstrating again that our experiment did work!
This was a fun and simple experiment to do with the girls.
I think the colours you get do depend somewhat on the concentration of your cabbage juice.
You could spend a little more time to do a more accurate experiment perhaps with older kids - making your own colour scale, and recording the results in a table.
However for my girls - aged 8 and 10, this was just a quick, fun experiment to do in the holidays.
Have you ever tried this?
Do you have any other simple and fun science experiments to recommend?