InterviewSolution
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InterviewSolution
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Explain why `E^(@)` for `Mn^(3+)// Mn^(@+)` couple is more positive than that for `Fe^(3+) //Fe^(2+) ` ( At. Nos. `Mn= 25, Fe= 26)` ? Or Why is `+2` oxidation state of manganese quite stable while the same is not true for iron ? `[Mn= 25 , Fe = 26]` |
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Answer» `._(25)Mn^(2+) = [Ar] 3d^(5), . _(25) Mn^(3+) =[Ar] 3d^(4), ._(26) Fe^(2+) = [ Ar] 3d^(6) , . _(26) Fe^(3+)= [ Ar] 3d^(5)` Thus, `Mn^(2+)` has more stable configuration than `Mn^(3+)` while `Fe^(3+)` has more stable then `Fe^92+)`. Consequently, large third ionisation enthalpy is required to change `Mn^(2+)` to `Mn^(3+)`. As `E^(@)` is the sum of enthalpy of atomisation, ionization enthalpy and hydration enthalpy, therefore, `E^(@)` for `Mn^(3+)//Mn^(2+)` couple is more positive than `Fe^(3+) //Fe^(2+)` . Note `,` The large positive `E^(@)` for `Mn^(3+)//Mn^(2+)` means that `Mn^(3+)` can be easily reduced to `Mn^(2+)` , i.e. `Mn^(3+)` is less stable . `E^(@)` value for `Fe^(3+) //Fe^2+)` is positive but small, i.e., `Fe^(3+)` can also be reduced to `Fe^(2+)` but less easily. Thus,`Fe^(3+)` is more stable than `Mn^(3+)` . It also explains why `+3` state of Mn is of little importance. |
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