Mangan

Manganates V f), [MnOJ", permanganates. Dark purple tetrahedral anion (electrolyte oxidation of [Mn04]. Powerful oxidizing agent... 

Manganates V), hypomanganatcs, [Mn04] . Deep blue ion (Mn02 in cone. K.OH [Mn04] plus excess [SOa] ). The salts are rapidly hydrolysed. 

Manganates III), again mixed-metal oxides present in the spinel Mn304, Mn Mn 204. 

Oxidation states can be used to establish the stoichiometry for an equation. Consider the reaction between the manganate(VII) (permanganate) and ethanedioate (oxalate) ions in acidic solution. Under these conditions the MnO faq) ion acts as an oxidising agent and it is reduced to Mn (aq), i.e. 

When either hydrogen ions or hydroxide ions participate in a redox half-reaction, then clearly the redox potential is alTected by change of pH. Manganate(Vir) ions are usually used in well-acidified solution, where (as we shall see in detail later) they oxidise chlorine ions. If the pH is increased to make the solution only mildly acidic (pH = 3-6), the redox potential changes from 1.52 V to about 1.1 V, and chloride is not oxidised. This fact is of practical use in a mixture of iodide and chloride ions in mildly acid solution. manganate(VII) oxidises only iodide addition of acid causes oxidation of chloride to proceed. 

Thus chloride ions are oxidised to chlorine by manganate( VIl) under standard conditions... 

Decolorise a solution of potassium manganate(Vll) acidified with dilute sulphuric acid. 

Silanes are very sensitive to attack by alkalis and will even react with water made alkaline by contact with glass this reaction is in marked contrast to the reactions shown by alkanes. Unlike alkanes, silanes are found to have marked reducing properties and will reduce, for example, potassium manganate(VII) to manganeseflV) oxide, and iron(III) to iron(II). 

The product is a solid yellow hydrated oxide. If prepared by a method in the absence of water, a black anhydrous product is obtained. Germanium(II) oxide is stable in air at room temperature but is readily oxidised when heated in air or when treated at room temperature with, for example, nitric acid, hydrogen peroxide, or potassium manganate(VII). When heated in the absence of air it disproportionates at 800 K ... 

This provides a method of estimating an iron(lll) salt. After reduction the iron(II) salt is titrated with manganate(VII) solution. 

Strong oxidising agents such as acidified potassium manganate(VII) oxidise NOj to the nitrate ion ... 

Pure oxygen is conveniently prepared by the thermal decomposition of potassium manganate(VII) ... 

Oxygen can be produced by certain reactions in solution, for example the oxidation of hydrogen peroxide by potassium manganate(VII) acidified with sulphuric acid ... 

Manganate(VII) is reduced to manganese(II) ion in acid solution (usually sulphuric acid) ... 

It has been shown in reaction (3) that all the evolved oxygen comes from the hydrogen peroxide and none from the manganate(VII) or water, by using H2 02 and determining the isotope in the evolved gas. 

The reaction with acidified potassium manganate(VII) is used in the quantitative estimation of hydrogen peroxide. 

In acid solution, the manganate(VII) ion is reduced to the manganesefll) ion with decolorisation ... 

Sulphites react with oxidising agents, for example mangan-ate(VII) and dichromate(VI) ... 

The "periodic acids and periodates are powerful oxidising agents and they will oxidise manganese to manganate(VlI). a reaction used to determine small quantities of manganese in steel. 

This oxide is obtained by adding potassium manganate(VII) to concentrated sulphuric acid, when it appears as a dark coloured oil which readily decomposes (explosively on heating) to manganese(IV) oxide and oxygen ... 

The green manganate(VI) is extracted with water, then oxidised to manganatefVII). This is usually carried out electrolytically. at an anode, but in the laboratory chlorine may be used ... 

Note that here chlorine is oxidising the manganate(Vl) to man-ganate(VlI) under more acid conditions, the latter oxidises chloride to chlorine, p. 103). 

Potassium manganate(VII) disproportionates on heating 2KMn04 K2Mn04 + Mn02 + O2... 

The manganate(VlI) ion slowly oxidises water, the essential reaction being... 

This reaction proceeds very slowly in absence of light, and aqueous solutions of potassium manganate(VII) are effectively stable for long periods if kept in dark bottles. 

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