Metal ion indicators, also known as chelating indicators or metallochromic indicators, are organic compounds that form colored complexes with metal ions.
They are used in complexometric titrations to detect the endpoint, which occurs when all the metal ions in the sample have reacted with the chelating agent.
Indicators are selected based on their ability to form weak complexes with the metal ions being analyzed.
illustration of Metal Ions indicators
(image may contain incorrect data, it is just for illustration purpose)
How They Work:
The formation of a colored complex between the metal ion and the indicator causes a visible color change.
During the titration, the chelating agent (e.g., EDTA) has a stronger affinity for the metal ions and displaces the indicator, breaking the weak complex and causing a color change.
When all metal ions have reacted with the chelating agent, any excess chelating agent reacts with the indicator, causing another color change that signals the endpoint of the titration.
This concise explanation covers the role and function of metal ion indicators in complexometric