Complexometric indicator: Difference between revisions

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{{short description|Chemical detector for metal ions in complexometric titrations}}

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 thanfrom the form existing outside of 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 [[indicator]]sindicators 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'''.

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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==

Complexometric indicators are water-soluble organic molecules. Some examples are:

* [[Eriochrome Black T]] for [[calcium]], [[magnesium]] and [[aluminium]]

* [[Calcein]] with [[Ethylenediaminetetraacetic acid|EDTA]] for calcium

* [[Xylenol orange]] for [[gallium]], [[indium]] and [[scandium]]

* [[Patton-Reeder Indicator]] with [[Ethylenediaminetetraacetic acid|EDTA]] for calcium with magnesium

* [[Methyl calcein blue]]

* [[Curcumin]] for [[boron]], that forms [[Rosocyanine]], although the red color change of curcumin also occurs for pH > 8.4

* [[Murexide]]

* [[Eriochrome Black T]] for [[calciumaluminium]], [[magnesiumcadmium]], [[zinc]], [[calcium]] and [[aluminiummagnesium]]

* [[Fast Sulphon Black]]

* [[Fast Sulphon Black]] with [[Ethylenediaminetetraacetic acid|EDTA]] for [[copper]]

* [[Eriochrome Red B]]

* [[Calcein]]

* [[Calcon]]

* [[Eriochrome blue-black B]]

* [[Eriochrome blue SE]]

* [[Hydroxynaphthol blue]]

* [[Methylthymol blue]]

* [[Phthalein purple]]

* [[Pyrogallol red]]

* [[3,3'-dimethylnaphthidine]]

* [[Chromazurol S]]

* [[Hematoxylin]] for [[copper]]

* [[Murexide]] for calcium and [[rare earths]], but also for [[copper]], [[nickel]], [[cobalt]], and [[thorium]]

* [[Naphthol Green B]]

* [[Xylenol orange]] for [[gallium]], [[indium]] and [[scandium]]

* [[1-(2-pyridilazo)-2-naphthol]] (PAN)

==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==

{{chem-stub}}

{{Reflist}}

[[Category:Analytical chemistry]]

==External links==

*{{Commonscatinline|Complexometric indicators}}

[[Category:Complexometric indicators| ]]