Standard electrode potential data are useful for understanding the suitability of an oxidant in a redox titration some half cell reactions and their standard potentials are given below
`MnO_(4)^(-)(aq)+8H^(+)(aq)+5e^(-)rarrMn^(2+)(Aq)+4H_(2)O(l)^(@)=1.51 V`
`Cr_(2)O_(7)^(2-)(Aq)+14 H^(+)(aq)+6e^(-)rarr2cr^(3+)(aq)+7H_(2)O(l),E^(2)=1.38 V`
`CI_(2)(g)+2e^(-)rarr2CI^(-)(aq),E^(@)=1.40 V`
Identify the incorrect statement regarding the qunatitavite estimation of gaseous `Fe(NO_(3))_(2)`

Options

A. `MnO_(4)^(-)` can be used in aqueous HCI
B. `Cr_(2)O_(7)^(2-)` can be used in aqueous HCI
C. `MnO_(4)^(-)` 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

B

Explanation

The reaction between `MnO_(4)^(-)` and HCI may be represented as follows
`2MnO_(4)^(-) (aq)+16H^(+) +10CI^(-) rarr 2Mn^(2+) (aq)+8H_(2)O(I)+5CI_(2)(g)`
Thus on the basis of this reaction following electrochemcial cell will be represented as
since `E_(cell)^(2)=e_(cathode)^(@) -E_(anode)^(2)`
`E_(cell)^(@)` is positive hence `triangle G^(@)` is negative thus above celll reaction is feasible but `MnO_(4)^(-1)` ion can oxidse `Fe^(2+)` to `Fe^(3+)` and `CI^(-)` to `CI_(2)` in aqueous medium also
Therefore for quantivative estimiation of aqueous `Fe(NO_(3))_(2)` it is not a suitable reagent