Standard electrode potentials are useful for judging whether an oxidant is suitable in a redox titration. Given: MnO4⁻ + 8H+ + 5e- - Mn²+ + 4H2O, E^o = 1.51 V Cr2O7²- + 14H+ + 6e- - 2Cr³+ + 7H2O, E^o = 1.38 V Fe³+ + e- - Fe²+, E^o = 0.77 V Cl2 + 2e- - 2Cl-, E^o = 1.40 V For the quantit

Question

Standard electrode potentials are useful for judging whether an oxidant is suitable in a redox titration. Given: MnO4⁻ + 8H+ + 5e- -> Mn²+ + 4H2O, E^o = 1.51 V Cr2O7²- + 14H+ + 6e- -> 2Cr³+ + 7H2O, E^o = 1.38 V Fe³+ + e- -> Fe²+, E^o = 0.77 V Cl2 + 2e- -> 2Cl-, E^o = 1.40 V For the quantitative estimation of aqueous Fe(NO3)2, identify the only incorrect statement.

Accepted Answer

MnO4⁻ can be used in aqueous HCl. A good oxidant for Fe²+ titration must oxidize Fe²+ (potential 0.77 V) without interference. In HCl, an oxidant with E^o above 1.40 V will also oxidize Cl- to Cl2, consuming the titrant and giving wrong results. MnO4⁻ (1.51 V) > 1.40 V, so it oxidizes Cl-; hence MnO4⁻ in HCl is unsuitable - that statement is incorrect. Cr2O7²- (1.38 V) < 1.40 V, so it does not appreciably oxidize Cl-, so it works in HCl. Both work in H2SO4 since sulphate is not oxidized.

Solution

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