Page 29 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202
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Neutral or weakly alkaline solutions

MnO4− + 4H+ + 3e          MnO2 (s) + 2H2O E0 = 1.69 V
                        Manganese dioxide

                                (brown solid)

Change in oxidation state of Mn: +7 to +4

               Eq wt = Mw / 3

               Strongly alkaline solutions (2 M NaOH)

MnO4− + e                 MnO42 −           E0 = + 0.56 V
                  manganate (green)

Change in oxidation state of Mn: +7 to +6

               Eq wt = Mw / 1

Applications in acidic solutions, 0.1M to 1M H2SO4

(Question: why not use HCl for acidity?)

The acid used for acidification is H2SO4 and not HCl as MnO4-
oxidizes Cl– in acid medium
For MnO4−/ Mn2+
                             E0 = +1.51 V

For Cl2 / Cl−                E0 = +1.36 V

2 MnO4− + 10Cl− + 16H+         2 Mn2+ + 5Cl2 + 8H2O

                     Direct Titrations

               Determination of reducing species

[1] Determination of Fe2+ salts e.g. FeSO4

MnO4− + 5Fe2+ + 8H+            Mn2+ + 5Fe3+ + 4H2O

Cl- Interference

If an iron sample has been dissolved in HCl or if SnCl2 has been
used to reduce Fe3+ to Fe2+,

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