Whether or not you celebrate Christmas, chances are you will be familiar with the Poinsetta plant (see image below). Poinstetta’s are traditional Christmas plants due to their deep red colour and originate from Mexico.


Image kindly sourced from: By André Karwath aka Aka – Own work, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=16584

Probably what you didn’t know though is that the deep red colour is called by a class of molecule called an anthocyanin (read more on anthocyanins here: https://en.wikipedia.org/wiki/Anthocyanin)

Anthocyanins are water soluble pigments that change colur according to the pH. The particular anthocyanin is Poinsetta’s will be red at a pH of less than 3. Between pH 3-4 it is colourless. A violet colour is seen at pH 4-7. Whist at pH 8-9 we see blue and finally above pH 9 the anthocyanin is green. 1

This means that it is possible to make your own indicator at home (or in school) using relatively low tech equipment. That said, like any experiment you carry out, you need to risk assess it and take responsibility for ensuring tht you carry out the work safely.

All you need to do is pick a few leaves, cut them up with scissors or just tear them (why?) and then boil them for a minute or two in water (why not for longer?)

The water should turn a red colour. Finally, use a sieve to strain the water and you will now have your very own home made indicator. Some anthrocyanin’s are used as natural food colours but I would not recommend ingesting the anthrocyanin you have extracted.

You should be able to find a range of household substances that you can add the indicator to to get a feel for the pH of them. For example, you may wish to try lemon or lime juice. How about white vinegar (why not brown?). What about washing up liquid, soap, bleach (be careful) or tooth paste?

If you have time you can also use this method to make some indicator from red cabbage – and then test the same substances to see if the colour changes are the same or different.

Are you aware of any other natural indicators? If so, please post about them below.

Dare I say it but could this be a possible IA?!

Have you tried this experiment? If so, I would love to see some photos of your results. Please post them below if you wish.

On, and a word of caution – before you go removing the Poinsetta leaves ….. check with the person who owns the plant that this is OK!


1 Read more here: http://www.compoundchem.com/2016advent/2016advent12/