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Why is the E^(Theta)value for the Mn^(3+...

Why is the `E^(Theta)`value for the `Mn^(3+)//Mn^(2+)` couple much more positive than that for `Cr^(3+)//Cr^(2+)` or`Fe^(3+)//Fe^(2+)`

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The large positive `E^(@)` value for `Mn^(3+) //Mn^(2+)` shows that `Mn^(2+)` is much more stable than `Mn^(3+)` . This is due to the fact that `Mn^(2+)` has the configuation `3d^(5)` whichis half - filled an hence is very stable. Thus, the third ionization energy of Mn will be very high. In fact, this is the reason that `+3` state of Mn is of little importance.
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(a) why is the E^(Theta) value for the Mn^(3+)//Mn^(2+) couple much more positivethan that for Cr^(3+)//Cr^(2+) or Fe^(3+) // Fe^(2+) ? Explain. (b) What is meant by 'disproportionation' of an oxidation state? Give example.

Why is the E^(Theta) value for the Mn^(3+)//Mn^(2+) couple much postive than for Cr^(3+)//Cr^(2+) or Fe^(3+)//Fe^(2+) ? Example

S_(1) : Mn^(2+) compounds more stable than Fe^(2+) towards oxidation to their +3 state. S_(2) : Titanium and copper both in the first series of transition metals exhibits +1 oxidation state most frequently. S_(3) : Cu^(+) ions is stable in aqueous solutions. S_(4) : The E^(0) value for the Mn^(3+)//Mn^(2+) couple much more positive than that for Cr^(3+)//Cr^(2+) or Fe^(3+)//Fe^(2+) ,

How would you account for the following? (i)The atomic radii of the metals of the third (5d) series of trasition elements are virtually the same as those of the corresponding members of the second (4d) series. (ii)The E^(@) value for the Mn^(3+)//Mn^(2+) couple is much more positive than that for Cr^(3+)//Cr^(2+) couple or Fe^(3+)//Fe^(2+) couple. (iii)The highest oxidation state of a metal is exhibited in itsoxide or fluoride.

How would you account for the following? (i) The atomic radii of the metals of the third (5d) series of transition elements are virtually the same as those of the corresponding member of the second (4d) serie (ii) The E^(@) value for the Mn^(3+)//Mn^(2+) couple is much more positive than that for Cr^(3+)//Cr^(2+) couple of Fe^(3+)//Fe^(2+) couple. (iii) The highest oxidation state of a metal is exhibited in its oxides or fluoride.

Why is the value for (Mn^(3+))/(Mn^(2+)) couple much more positive than that for (Cr^(3+))/(Cr^(2+)) or (Fe^(3+))/(Fe^(2+)) ? Explain

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