Standard reduction potentials help judge whether an oxidizing agent is appropriate in a redox titration. The following half-reactions and their standard potentials are given:

MnO4-(aq) + 8H+(aq) + 5e- → Mn2+(aq) + 4H2O(l) E° = 1.51 V
Cr2O7²-(aq) + 14H+(aq) + 6e- → 2Cr3+(aq) + 7H2O(l) E° =

Question

Standard reduction potentials help judge whether an oxidizing agent is appropriate in a redox titration. The following half-reactions and their standard potentials are given:

MnO4-(aq) + 8H+(aq) + 5e- → Mn2+(aq) + 4H2O(l) E° = 1.51 V
Cr2O7²-(aq) + 14H+(aq) + 6e- → 2Cr3+(aq) + 7H2O(l) E° = 1.38 V
Fe3+(aq) + e- → Fe2+(aq) E° = 0.77 V
Cl2(g) + 2e- → 2Cl-(aq) E° = 1.40 V

For the volumetric estimation of Fe(NO3)2, which one of the following statements is not correct?

Accepted Answer

MnO4- may be employed in aqueous HCl. MnO4- (E=1.51 V) is strong enough to oxidize Cl- (1.40 V), so in HCl it consumes acid by liberating Cl2, giving erroneous results. Cr2O7^2- (1.38 V) cannot oxidize Cl-, so it is safe in HCl. Hence 'MnO4- may be employed in aqueous HCl' is the incorrect statement.

Solution

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