InterviewSolution
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InterviewSolution
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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)`A. `MnO_(4)^(-)` can be used in aqeuous HClB. `Cr_(2)O_(7)^(2-)` can be used in aqueous HClC. `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)`. |
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Answer» Correct Answer - 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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