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The electrode with reaction :Cr(2)O(7)^(...

The electrode with reaction `:Cr_(2)O_(7)^(2-)(aq)+14H^(o+)(aq)+6e^(-) rarr 2Cr^(3+)(aq)+7H_(2)O` can be represented as

A

`MnO_(4)^(-)` can be used in aqeuous HCl

B

`Cr_(2)O_(7)^(2-)` can be used in aqueous HCl

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)`.

Text Solution

Verified by Experts

The correct Answer is:
A
When `MnO_(4)^(-)` is used in a queous HCl, `MnO_(2)` reacts wit `Fe^(2+)` as well as with HCl as explained below.
`MnO_(4)^(-)+5Fe^(2+)+8H^(+)rarr5Fe^(3+)+ 4H_(2)O+Mn^(2+)`
`E_("Cell")^(@)=1.51- 0.77=0.74Vgt0`
`MnO_(4)^(-)+16H^(+)+10Cl^(-)rarrMn^(2+)+8H_(2)O+5Cl_(2)`
`E_("cell"^(@)=1.51-0.77=0.74Vgt0`
As such `MnO_(4)^(-)` cannot be used for the quantitative estimation of aqueous `Fe(NO_(3))_(2)` . Thus option A is not correct. Similarly we can show that `Cr_(2)O_(7)^(2-)` will react with `Fe^(2+)` but not with HCl.
`Cr_(2)O_(7)^(2-)+6Fe^(2+)+14H^(+)rarr2Cr^(3+)+7H_(2)O+6 Fe^(3+)`
`E_("cell")^(@)=1.38-0.77=0.61Vgt0`
`Cr_(2)O_(7)^(2-)+ 6Cl^(-)+14H^(+)rarr2Cr^(3+)+7H_(2)O^(+)3Cl_(2)`
`E_("cell")^(@)=1.38-1.40=-0.02Vlt0`
Thus, the normal reactions is not possible Thus `Cr_(2)O^(7)^(-)` in aqueous HCl can be used for the quantitative estimation of aqueous `Fe(NO_(3))_(2)`.
Option C and D are correct.
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