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Give reasons : (a) E^(@) value for Mn^(3+)//Mn^(2+) couple is much more positive than that for Fe^(3+)//Fe^(2+). (b) Iron has higher enthalpy of atomisation than that of copper. ( c ) Sc^(3+) is colourless in aqueous solution whereas Ti^(3+) is coloured. |
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Answer» Solution :(a) `E^(@)` value for `Mn^(3+)//Mn^(2+)` couple is much more positive than that for `Fe^(3+)//Fe^(2+)`. Electronic configurations of `Mn^(3+)` is `-3d^(4)` and that of `Mn^(2+)` is `-3d^(5)`. Thus `Mn^(3+)` has a tendency to gain one electron and change to more STABLE half-filled configuration to give `Mn^(2+)`. Thus it has a HIGHER value of `E^(@)`. Electronic configurations of `Fe^(3+)` is `-3d^(5)` and that of `Fe^(2+)` is `-3d^(6).Fe^(3+)` has a more stable half-filled configuration and has no tendency to gain an electron to change into `Fe^(2+)`. Therefore `E^(@)` value for `Mn^(3+)//Mn^(2+)` couple is much more positive than for `Fe^(3+)//Fe^(2+)`. (b) Iron has higher enthalpy of atomisation than that of copper. Enthalpy of atomisation depends upon the number of electrons in the outermost orbit. Iron has a higher enthalpy of atomisation than that of copper. ( c ) `SC^(3+)` is colourless in aqueous solution whereas `Ti^(3+)` is coloured. Colour of a transition metal compound is due to d-d transition. Configuration of `Sc^(3+)` is [Ar]. There are no d-electrons and therefore there is no possibility of d-d transitions. Hence `Sc^(3+)` is colourless in aqueous solution. Configuration of `Ti^(3+)` is `3d^(1)`. There is a possibility of d-d transition. Hence this is coloured. |
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