Yesterday we finally got around to doing an experiment, using red cabbage to find the pH of various household liquids. Pouring boiling water over red cabbage and leaving it for 30 minutes or so produces a purple liquid (the indicator) that can be used to find out whether a liquid is acidic or basic. The indicator changes colour depending on the amount of hydrogen (the H in pH) in the liquid. The pH scale goes from 0 to 14, with 7 as neutral. Below 7 indicates an acid, above 7 indicates a base.
We decided to line up glasses with various liquids in them in what we thought would beΒ acids to bases, with plain water (neutral) in the middle.

All substances were diluted in water. From left to right we had – vinegar, lemon juice, apple juice, sugar water, plain water, milk, dishwashing liquid, washing powder and bicarbonate of soda. We were unsure how the slight colour of some of the substances (especially the dishwashing liquid) might affect the results. In the end it didn’t make too much difference – the milk was the hardest to read, but the others were OK.
The red cabbage indicator made the water purple, as there was no reaction to change the colour, but we were unprepared for how quickly and dramatically the colours changed, and how beautiful the colours were! Generally acids range from reds to pinks, and bases from blues to greens/yellows.

It was quite exciting! π
As you can see, we got some wrong. The sugar water needed to go to the bases side, and the dishwashing liquid to the acids. The washing powder was extremely basic, and we were a bit undecided on the vinegar and lemon juice, but eventually decided to swap them round – the lemon juice seemed a bit redder. Here’s the finished line up.

It’s an easy experiment which doesn’t really take that long for the practical work. Part of science learning this year is improving the documentation of experiments, so there’ll still be some research to finish writing it up. It was a satisfying end to the week, though!
Here’s another view of the lovely colours, with the jug of indicator tucked into the top right corner…
