Analytical Chemistry of Mn III

However, compared to Mn and Mn02, Mn is on a convex point indicating its tendency to disproportionate, according to  

This shows that in order to prepare Mn(IlI) solution, an excess of acid and of Mn ions should be present to favour the back reaction of (12.3). 

Prepare 0.05 M MnS04 solution in 3 M sulphuric acid. Gradually add to an aliquot of the solution freshly prepared 0.02 M KMn04 until the wine colour of Mn(IlI) is fully 

Hence manganese (III) sulphate solution can be standardised widi a standard solution of a reductant eg iron (II) in acid solution. The end-point can be found potentiometrically or by using a suitable redox indicator eg ferroin (iron (II) complex with 1,10-phenanthroline) which is red but turns blue when oxidised. 

Pipette 25.0 cm of standard 0.020 M Fe(II) solution into a conical flask. Add 25 cm dilute H2SO4, 5 cm H3PO4 and a few drt s of ferroin indicator. Titrate with die prepared Mn(lII) solution in the burette until die colour suddenly changes to blue. Repeat the titration and calculate from the average titre the concentration of Mn(IlI) in mol dm.  

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The analytical chemistry of Mn(III) solutions and its reactions with ascorbic acid and with hydrazine and hydrazinium salts are discussed in 112(1987)511. The reference also gives... 

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