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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