Standard electrode potential data are useful for understanding the suitability of an oxidant in a redox titration. Some half cell reaction and their standard potentials are given below:
`MnO_(4)^(-)(aq) +8H^(+)(aq) +5e^(-) rarr Mn^(2+)(aq) +4H_(2)O(l) E^(@) = 1.51V`
`Cr_(2)O_(7)^(2-)(aq) +14H^(+) (aq) +6e^(-) rarr 2Cr^(3+)(aq) +7H_(2)O(l), E^(@) = 1.38V`
`Fe^(3+) (aq) +e^(-) rarr Fe^(2+) (aq), E^(@) = 0.77V`
`CI_(2)(g) +2e^(-) rarr 2CI^(-)(aq), E^(@) = 1.40V`
Identify the only correct statement regarding quantitative estimation of aqueous `Fe(NO_(3))_(2)`

Options

A. `MnO_(4)^(c-)` can be used in aqueous `HCl`
B. `CrO_(4)^(2-)` can be used in aqueous `HCl`
C. `MnO_(4)^(c-)` can be used in aqueous `H_(2)SO_(4)`
D. `Cr_(2)O_(7)^(2-)` can be used in aqueous `H_(2)SO_(4)`

Answer

a

Explanation

The reaction between `MnO_(4)^(c-)` and `HCl` may be represented as follows`:`
`2MnO_(4)^(c-)(aq)+16H^(o+)+10Cl^(c-) rarr 2Mn^(2+)(aq)+8H_(2)O(l) +5Cl_(2)(g)`
Thus, on the basis of this reaction following electrochemical cell will be represented `:`
`Pt, Cl_(2)(g)(1atm)|Cl^(c-)(aq)||MnO_(4)^(c-)(g)|Mn^(2+)(aq)`
Hence, `E^(c-)._(cell)=E^(c-)._(cathode)-E^(c-).(anode)`
From the given data , `E^(c-)._(cell)=1.51-1.40=0.11V`
`E^(c-)` cell is positive, hence `DeltaG^(c-)` is negative. Thus, the above cell reaction is feasible but `MnO_(4)^(c-)` ion can oxidize, `Fe^(2+)` to `Fe^(3+)` and `Cl^(c-)` to `Cl_(2)` in aqueous medium also . Therefore, for quantitative estimation of aqueous `Fe(NO_(3))_(2)` it is not a suitable reagent.