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{{short description|Indicator which undergoes a definite color change at a specific electrode potential}} |
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{{refimprove|date=December 2009}} |
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A '''redox indicator''' (also called an '''oxidation-reduction indicator''') is an indicator which undergoes a definite color change at a specific [[electrode potential]]. |
A '''redox indicator''' (also called an '''oxidation-reduction indicator''') is an indicator which undergoes a definite color change at a specific [[electrode potential]]. |
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The requirement for fast and reversible color change means that the oxidation-reduction [[Chemical equilibrium|equilibrium]] for an indicator [[redox system]] needs to be established very quickly. Therefore, only a few classes of organic redox systems can be used for indicator purposes.<ref>{{cite encyclopedia|Ullmann's Encyclopedia of Industrial Chemistry| |
The requirement for fast and reversible color change means that the oxidation-reduction [[Chemical equilibrium|equilibrium]] for an indicator [[redox system]] needs to be established very quickly. Therefore, only a few classes of organic redox systems can be used for indicator purposes.<ref>{{cite encyclopedia| encyclopedia = Ullmann's Encyclopedia of Industrial Chemistry|author=Ram W. Sabnis |author2=Erwin Ross |author3=Jutta Köthe |author4=Renate Naumann |author5=Wolfgang Fischer |author6=Wilhelm-Dietrich Mayer |author7=Gerhard Wieland |author8=Ernest J. Newman |author9=Charles M. Wilson |title=Indicator Reagents|year=2009|publisher=Wiley-VCH|place=Weinheim|doi=10.1002/14356007.a14_127.pub2|isbn=978-3-527-30673-2}}</ref> |
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There are two common classes of redox indicators: |
There are two common classes of redox indicators: |
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* [[metal complex]]es of [[phenanthroline]] and [[bipyridine]]. In these systems, the metal changes oxidation state. |
* [[metal complex]]es of [[phenanthroline]] and [[bipyridine]]. In these systems, the metal changes oxidation state. |
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* [[organic redox system]]s such as [[ |
* [[organic redox system]]s such as [[methylene blue]]. In these systems, a proton participates in the redox reaction. Therefore, sometimes redox indicators are also divided into two general groups: independent or dependent on [[pH]]. |
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The most common redox indicator are organic compounds]]. |
The most common redox indicator are [[organic compounds]]. |
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Redox Indicator example: |
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The molecule 2,2'- Bipyridine is a redox Indicator. In solution, it changes from light blue to red at an electrode potential of 0.97 V. |
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==pH independent== |
==pH independent== |
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|align=center bgcolor=white|colorless |
|align=center bgcolor=white|colorless |
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|- |
|- |
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|1,10-Phenanthroline iron(II) sulfate complex (Ferroin) |
|1,10-Phenanthroline iron(II) sulfate complex ([[Ferroin]]) |
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|align=center| +1.06 |
|align=center| +1.06 |
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|align=center bgcolor=cyan|cyan |
|align=center bgcolor=cyan|cyan |
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| +0.97 |
| +0.97 |
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|align=center bgcolor=#CCFF00|yellow-green |
|align=center bgcolor=#CCFF00|yellow-green |
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|align=center bgcolor= |
|align=center bgcolor=cyan|cyan |
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|- |
|- |
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|[[ |
|[[o-Dianisidine]] |
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|align=center| +0.85 |
|align=center| +0.85 |
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|align=center bgcolor=red|red |
|align=center bgcolor=red|red |
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!E<sup>0</sup>, V |
!E<sup>0</sup>, V |
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at pH=0 |
at pH=0 |
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!E |
!E, V |
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at pH=7 |
at pH=7 |
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!Color of |
!Color of |
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|align=center bgcolor=white|colorless |
|align=center bgcolor=white|colorless |
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|- |
|- |
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|[[Safranin |
|[[Safranin|Safranin '''T''']] |
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|align=center bgcolor=white| +0.24 |
|align=center bgcolor=white| +0.24 |
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|align=center bgcolor=white| -0.29 |
|align=center bgcolor=white| -0.29 |
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==See also== |
==See also== |
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*[[Analytical chemistry|Chemical analysis]] |
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*[[pH indicator]] |
*[[pH indicator]] |
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*[[Complexometric indicator]] |
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==External links== |
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{{DEFAULTSORT:Redox Indicator}} |
{{DEFAULTSORT:Redox Indicator}} |
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[[Category:Redox indicators]] |
[[Category:Redox indicators]] |
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[[Category:Physical chemistry]] |
[[Category:Physical chemistry]] |
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[[it:Indicatore (chimica)#Indicatori di ossido-riduzione]] |
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Latest revision as of 14:59, 28 September 2023
 | This article needs additional citations for verification. (December 2009) |
A redox indicator (also called an oxidation-reduction indicator) is an indicator which undergoes a definite color change at a specific electrode potential.
The requirement for fast and reversible color change means that the oxidation-reduction equilibrium for an indicator redox system needs to be established very quickly. Therefore, only a few classes of organic redox systems can be used for indicator purposes.[1]
There are two common classes of redox indicators:
- metal complexes of phenanthroline and bipyridine. In these systems, the metal changes oxidation state.
- organic redox systems such as methylene blue. In these systems, a proton participates in the redox reaction. Therefore, sometimes redox indicators are also divided into two general groups: independent or dependent on pH.
The most common redox indicator are organic compounds. Redox Indicator example: The molecule 2,2'- Bipyridine is a redox Indicator. In solution, it changes from light blue to red at an electrode potential of 0.97 V.
pH independent
[edit]| Indicator | E0, V | Color of Oxidized form | Color of Reduced form |
|---|---|---|---|
| 2,2'-bipyridine (Ru complex) | +1.33 | colorless | yellow |
| Nitrophenanthroline (Fe complex) | +1.25 | cyan | red |
| N-Phenylanthranilic acid | +1.08 | violet-red | colorless |
| 1,10-Phenanthroline iron(II) sulfate complex (Ferroin) | +1.06 | cyan | red |
| N-Ethoxychrysoidine | +1.00 | red | yellow |
| 2,2`-Bipyridine (Fe complex) | +0.97 | cyan | red |
| 5,6-Dimethylphenanthroline (Fe complex) | +0.97 | yellow-green | cyan |
| o-Dianisidine | +0.85 | red | colorless |
| Sodium diphenylamine sulfonate | +0.84 | red-violet | colorless |
| Diphenylbenzidine | +0.76 | violet | colorless |
| Diphenylamine | +0.76 | violet | colorless |
| Viologen | -0.43 | colorless | blue |
pH dependent
[edit]| Indicator | E0, V
at pH=0 |
E, V
at pH=7 |
Color of
Oxidized form |
Color of
Reduced form |
|---|---|---|---|---|
| Sodium 2,6-Dibromophenol-indophenol
or Sodium 2,6-Dichlorophenol-indophenol |
+0.64 | +0.22 | blue | colorless |
| Sodium o-Cresol indophenol | +0.62 | +0.19 | blue | colorless |
| Thionine (syn. Lauth's violet) | +0.56 | +0.06 | violet | colorless |
| Methylene blue | +0.53 | +0.01[2] | blue | colorless |
| Indigotetrasulfonic acid | +0.37 | -0.05 | blue | colorless |
| Indigotrisulfonic acid | +0.33 | -0.08 | blue | colorless |
| Indigo carmine
(syn. Indigodisulfonic acid |
+0.29 | -0.13 | blue | colorless |
| Indigomono sulfonic acid | +0.26 | -0.16 | blue | colorless |
| Phenosafranin | +0.28 | -0.25 | red | colorless |
| Safranin T | +0.24 | -0.29 | red-violet | colorless |
| Neutral red | +0.24 | -0.33 | red | colorless |
See also
[edit]References
[edit]- ^ Ram W. Sabnis; Erwin Ross; Jutta Köthe; Renate Naumann; Wolfgang Fischer; Wilhelm-Dietrich Mayer; Gerhard Wieland; Ernest J. Newman; Charles M. Wilson (2009). "Indicator Reagents". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a14_127.pub2. ISBN 978-3-527-30673-2.
- ^ HEWITT, LF. "Oxidation-Reduction Potentials in Bacteriology and Biochemistry." Oxidation-Reduction Potentials in Bacteriology and Biochemistry. Edn 6 (1950).