Complexometric indicator
A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions.[1] It forms a weak complex with the ions present in the solution, which has a significantly different color from the form existing outside the complex. Complexometric indicators are also known as pM indicators.[2]
Examples
Complexometric indicators are water-soluble organic molecules. Some examples are:
- Calcein with EDTA for calcium
- Patton-Reeder Indicator with EDTA for calcium with magnesium
- Curcumin for boron, that forms Rosocyanine, although the red color change of curcumin also occurs for pH > 8.4
- Eriochrome Black T for aluminium, cadmium, zinc, calcium and magnesium
- Fast Sulphon Black with EDTA for copper
- Hematoxylin for copper
- Murexide for calcium and rare earths, but also for copper, nickel, cobalt, and thorium
- Xylenol orange for gallium, indium and scandium
Redox indicators
In some settings, when the titrated system is a redox system whose equilibrium is influenced by the removal of the metal ions, a redox indicator can function as a complexometric indicator.
References
- ^ Flaschka, H.; Schwarzenbach, G.; Schwarzenbach, Gerold (1969). Complexometric titrations. London: Methuen. ISBN 0-416-19290-4.
- ^ M. A. Malati (1999). Experimental Inorganic/Physical Chemistry: An Investigative, Integrated Approach to Practical Project Work (Horwood Series in Chemical Science). Albion/Horwood Pub. p. 20. ISBN 1-898563-47-0.
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