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

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

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Much larger third ionisation energy of Mn (where the required change is `d^2` to `d^4`) is mainly responsible for this. This also explains why the `+3` state Of Mn is of little importance.
`E_((Mn^(3+))/(Mn^(2+))^(ɵ))gtE_((Fe^(3+))/(Fe^(2+))^(ɵ))gtE_((Cr^(3+))/(Cr^(2+))^(ɵ))`
`(+1.57gt+0.77gt -0.41V)`
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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 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 its oxide 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

Assign reasons for the following : (i) The enthalpies of atomisation of transition elements are high. (ii) The transition metals and many of their compounds act as good catalyst. (iii) From element to element the actinoid contraction is greater than the lanthanoid contraction. (iv) The E^(@) value for the Mn^(3+)//Mn^(2+) couple is much more positive than that for Cr^(3+)//Cr^(2+) . (v) Scandium (Z = 21) does not exhibit variable oxidation states and yet it is regarded as transition element.

Explain why E^(@) for Mn^(3+)//Mn^(2+) couple is more positive than that for Fe^(3+)//Fe^(2+) (At. Nos. Mn=25,Fe=26)?

E_(Mn^(3+)//Mn^(2+))^@ is highly positive than that of E_(Cr^(3+)//Cr^(2+))^@orE_(Fe^(3+)//Fe^(2+))^@ because

Give reason for the folloiwng : (a) E_("value")^(@) for Mn^(3+)//Mn^(2+) couple is much more positive than that of Fe^(3+)//Fe^(2+) couple. (b) Sc^(3+) is colourless in aqueous solution whereas Ti^(3+) is coloured.

Assign reasons for the following: (a) Ce^(3+) can easily be oxidised to Ce^(4+) (b) E^(Theta) for Mn^(3+) | Mn^(2+) couple is more positive than Fe^(3+) | Fe^(2+) Explain the following : (a) Zr and Hf exhibit similar properties. (b) The colour of K_2Cr_2O_7 solution changes with the change in pH value of the solution .

Why E^(-) values for Mn, Ni and Zn are more negative than expected?

Assertion: E^(@) for Mn^(3+)//Mn^(2+) is more positive than Cr^(3+)//Cr^(2+) Reason: The third ionisation energy of Mn is larger than that of Cr .

Why Fe^(2+) has smaller radius than Mn^(2+) ?

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