pH and colours workshop with Dr Lee Wai Leng

8 July 2019

Trying to guess whether the liquid is acidic or alkaline can be tough. Imagine this: there is a transparent liquid on the table and it could be just plain water or detergent. We know there is a tendency for people to test everything with their tongues but in this kind of situation it is best to use a measuring instrument. Who knows? The innocent-looking clear liquid could be a detergent or acid.

But what if you do not have any testing equipment with you? No, you do not need to go back to tongue testing. There is another way and that is through telling colours! Did you know that there are many natural ingredients out there that can be used as a universal indicator? To put it simply, it is a mixture of dyes that changes colour gradually over a range of pH.

Among the ingredients that can be used as universal indicators include red cabbage, pea flower and onion! As to why these ingredients can be used to indicate pH value, Dr Lee Wai Leng explains in her pH and colours workshop at 100 Lambs Homeschool, Johor Bahru, that they contain anthocyanin which can detect the hydrogen ions and hydroxyl ions in a solution.

At a lower pH, more hydrogen ions are in the solution. Hence, resulting in a red colour that indicates the liquid as acidic. And if it has a higher pH, that means there are more hydroxyl ions in the solution. The liquid will appear purplish, meaning it is alkaline. For neutral solutions, the concentration of both hydrogen ions and hydroxyl ions are balanced. So, the colour we will be seeing is a greenish-yellow.

Well, that is a lot to process, isn’t it? Rather than just memorising what colour means what, Dr Lee lets the students make their own pH indictor using red cabbage juice in the workshop. After that, they were required to build a pH chart whereby the students had to name the colours and determine for themselves whether the solution is acidic or alkaline.