Analytical Chemistry

Measure Twice

What is a chemical indicator?

As we mentioned, for a titration to be successful there must be some indication of when it has finished. Chemical indicators are a common way of determining whether a titration is complete. In acid–base titrations, chemical indicators are typically small molecules whose colors change depending on the pH of the solution (or, in other words, on their protonation state). In other cases, the indicator may change color based on whether it is coordinated to another species in a solution. It is also possible to use a device like a pH-sensitive electrode to determine when the titration has ended; this doesn’t rely on you (or another person) being able to notice a visible change in the color of the solution. Such a device can be more accurate, since it doesn’t rely on a qualitative interpretation of a color change.


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