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A '''complexometric indicator''' is an [[ionochromism|ionochromic]] [[dye]] that undergoes a definite color change in presence of specific metal [[ion]]s.<ref name="isbn0-416-19290-4">{{cite book |author1=Flaschka, H. |author2=Schwarzenbach, G. |author3=Schwarzenbach, Gerold |title=Complexometric titrations |publisher=Methuen |___location=London |year=1969 |isbn=0-416-19290-4 }}</ref> It forms a weak [[complex (chemistry)|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.<ref name="isbn1-898563-47-0">{{cite book |author=M. A. Malati |title=Experimental Inorganic/Physical Chemistry: An Investigative, Integrated Approach to Practical Project Work (Horwood Series in Chemical Science) |publisher=Albion/Horwood Pub |year=1999 |page=20 |isbn=1-898563-47-0 }}</ref>
==Complexometric titration==
In [[analytical chemistry]], complexometric indicators are used in [[complexometric titration]] to indicate the exact moment when all the metal ions in the solution are sequestered by a [[chelating agent]] (most usually [[EDTA]]). Such indicators are also called '''metallochromic indicators'''.
The indicator may be present in another liquid phase in equilibrium with the titrated phase, the indicator is described as '''extraction indicator'''.
Some complexometric indicators are sensitive to air and are destroyed. When such solution loses color during titration, a drop or two of fresh indicator may have to be added.
==Examples==
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