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Standard electrode potential data are us...

Standard electrode potential data are useful for understanding the stability of an oxidant in a redox titration . Some half reactions and their standard potentials are given below :
`MnO_(4)^(-)(aq)+8H^(+)(g)+5e^(-)toMn^(2+)(aq)+4H_(2)O(l)E^(@)=1*51V`
`Cr_(2)O_(7)^(2-)(aq)+14H^(+)aq)+6e^(-)to2Cr^(3+)(aq)+7H_(2)+(l)E^(@)=1*38V`
`Fe^(3+)(aq)e^(-)toFe^(2+)(aq) " " E^(@)=0*77V`
`Cl_(2)(g)+2e^(-)to2Cl^(-)(aq) " " E^(@)=1*40V`
Identify the only incorrect statement regarding the quantitative estimation of aqueous `Fe(NO_(3))_(2)`.

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)`

Text Solution

Verified by Experts

The correct Answer is:
a
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.
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