Difference between revisions of "Potassium hypomanganate"
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'''Potassium hypomanganate''', K<sub>3</sub>MnO<sub>4</sub>, also known as '''potassium manganate(V)''', is a bright blue salt and a rare example of a manganese(V) compound. It is formed: | '''Potassium hypomanganate''', K<sub>3</sub>MnO<sub>4</sub>, also known as '''potassium manganate(V)''', is a bright blue salt and a rare example of a manganese(V) compound. It is formed: | ||
| − | *by the reduction of [[potassium permanganate]] with excess [[potassium sulfite]];<ref name="C&W">{{Cotton&Wilkinson4th|page=746}}.</ref><ref name="G&E">{{Greenwood&Earnshaw1st| | + | *by the reduction of [[potassium permanganate]] with excess [[potassium sulfite]];<ref name="C&W">{{Cotton&Wilkinson4th|page=746}}.</ref><ref name="G&E">{{Greenwood&Earnshaw1st|pages=1221–22}}.</ref> |
::MnO{{su|b=4|p=−}} + SO{{su|b=3|p=2−}} + H<sub>2</sub>O → MnO{{su|b=4|p=3−}} + SO{{su|b=4|p=2−}} + {{nowrap|2 H<sup>+</sup>}} | ::MnO{{su|b=4|p=−}} + SO{{su|b=3|p=2−}} + H<sub>2</sub>O → MnO{{su|b=4|p=3−}} + SO{{su|b=4|p=2−}} + {{nowrap|2 H<sup>+</sup>}} | ||
*by [[disproportionation]] when [[manganese dioxide]] is dissolved in a concentrated solution of [[potassium hydroxide]];<ref name="C&W"/> | *by [[disproportionation]] when [[manganese dioxide]] is dissolved in a concentrated solution of [[potassium hydroxide]];<ref name="C&W"/> | ||
::{{nowrap|2 MnO<sub>2</sub>}} + {{nowrap|3 OH<sup>−</sup>}} → MnO{{su|b=4|p=3−}} + MnO(OH) + H<sub>2</sub>O | ::{{nowrap|2 MnO<sub>2</sub>}} + {{nowrap|3 OH<sup>−</sup>}} → MnO{{su|b=4|p=3−}} + MnO(OH) + H<sub>2</sub>O | ||
| − | The hypomanganate anion is unstable with respect to disproportionation in all but the most alkaline of solutions. | + | The hypomanganate anion is unstable with respect to disproportionation in all but the most alkaline of solutions and, even then, its stability is only kinetic, not thermodynamic.<ref name="G&E"/><ref>{{RubberBible62nd|page=D-134}}.</ref> |
:MnO{{su|b=4|p=2−}} + e<sup>−</sup> {{eqm}} MnO{{su|b=4|p=3−}} ''E'' = +0.27 V | :MnO{{su|b=4|p=2−}} + e<sup>−</sup> {{eqm}} MnO{{su|b=4|p=3−}} ''E'' = +0.27 V | ||
:MnO{{su|b=4|p=3−}} + e<sup>−</sup> + {{nowrap|4 H<sub>2</sub>O}} {{eqm}} MnO<sub>2</sub> + {{nowrap|6 OH<sup>−</sup>}} ''E'' = +0.96 V | :MnO{{su|b=4|p=3−}} + e<sup>−</sup> + {{nowrap|4 H<sub>2</sub>O}} {{eqm}} MnO<sub>2</sub> + {{nowrap|6 OH<sup>−</sup>}} ''E'' = +0.96 V | ||
| + | However, K<sub>3</sub>MnO<sub>4</sub> has been cocrystallized with Ca<sub>2</sub>Cl(PO<sub>4</sub>), allowing the study of the [[Ultraviolet–visible spectroscopy|UV–visible spectrum]] of the hypomanganate ion.<ref name="C&W"/> | ||
==References== | ==References== | ||
Revision as of 09:24, 26 June 2010
| Potassium hypomanganate | |
|---|---|
| IUPAC name | potassium manganate(V) potassium tetraoxidomanganate(3−) |
| Properties | |
| Chemical formula | K3MnO4 |
| Molar mass | 236.23 g mol−1 |
| Related compounds | |
| Other anions | Potassium manganate Potassium permanganate |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
Potassium hypomanganate, K3MnO4, also known as potassium manganate(V), is a bright blue salt and a rare example of a manganese(V) compound. It is formed:
- by the reduction of potassium permanganate with excess potassium sulfite;[1][2]
- MnO−4 + SO2−3 + H2O → MnO3−4 + SO2−4 + 2 H+
- by disproportionation when manganese dioxide is dissolved in a concentrated solution of potassium hydroxide;[1]
- 2 MnO2 + 3 OH− → MnO3−4 + MnO(OH) + H2O
The hypomanganate anion is unstable with respect to disproportionation in all but the most alkaline of solutions and, even then, its stability is only kinetic, not thermodynamic.[2][3]
- MnO2−4 + e− ⇌ MnO3−4 E = +0.27 V
- MnO3−4 + e− + 4 H2O ⇌ MnO2 + 6 OH− E = +0.96 V
However, K3MnO4 has been cocrystallized with Ca2Cl(PO4), allowing the study of the UV–visible spectrum of the hypomanganate ion.[1]
References
- ↑ 1.0 1.1 1.2 Cotton, F. Albert; Wilkinson, Geoffrey Advanced Inorganic Chemistry, 4th ed.; Wiley: New York, 1980; p 746. ISBN 0-471-02775-8.
- ↑ 2.0 2.1 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 1221–22. ISBN 0-08-022057-6.
- ↑ CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p D-134. ISBN 0-8493-0462-8.
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