We can classify different solutions depending on their acidic and basic properties. We
define a pH scale to do this, ranging from value of well below 0 to 14 or higher. Solutions are acidic if they have
a pH below 7, and basic if their pH is above 7. pH 7 is a neutral solution.
Indicators are really useful tools to tell whether a solution we have is acidic or basic. They
have excellent properties in which they change colour depending on the pH of the solution
they are in. They achieve this by subtle changes to the molecule that gives rise to their
colour when exposed to the different acidic/basic environments.
Red cabbage and turmeric [labelled above as curry powder] are just two examples many useful natural indicators.
Turmeric displays two colours depending on whether it is exposed to an acidic or basic
solution. The molecule responsible for the colourful properties of turmeric is curcumin:
The subtle change in the structure of the molecule gives rise to the colour change from
yellow to red when in acidic and basic solutions. Therefore, turmeric lends itself as a really
useful, natural indicator!
Red cabbage indicator is even more useful, as it displays a range of colours which can be
compared to a colour chart to determine not only if the solution is acidic or basic, but the
rough pH of the solution.