(a) (i) Which is stronger reducing agent Cr^(2+) or Fe^(2+) and why? (ii) Explain why Cu^(+) ion is not stable in aqueous solutions. (iii) Explain why Ce^(4+) is a strong oxidising agent. (b) Describe the oxidising property of KMnO_(4) in neutral or faintly alkaline medium for its reaction with iodide ions and thiosulphate ions.

(a) (i) Which is stronger reducing agent Cr^(2+) or Fe^(2+) and why?

1.	(a) (i) Which is stronger reducing agent Cr^(2+) or Fe^(2+) and why? (ii) Explain why Cu^(+) ion is not stable in aqueous solutions. (iii) Explain why Ce^(4+) is a strong oxidising agent. (b) Describe the oxidising property of KMnO_(4) in neutral or faintly alkaline medium for its reaction with iodide ions and thiosulphate ions.
Answer» Solution :(a) (i) `Cr^(2+)` has outer electronic configuration `3D^(4)` and `Fe^(2+)` has outer electronic configuration `3d^(6)`. `Fe^(2+)` after losing one electron will have stable half-filled configuration `3d.^(5)`. Hence, `Fe^(2+)` has greater tendency to lose electron or to act as REDUCING agent. (ii) `Cu^(+)` ion does not have sufficiently negative value of heat of hydration. Therefore, `Cu^(+)` is not stable in aqueous solution. Moreover, it UNDERGOES disproportionation as : `2Cu^(+)toCu^(2+)+Cu` (iii) Although, `Ce^(4+)` is stable due to its noble gas configuration it acts as a strong oxidising agent because in doing so it reverts to the common +3 oxidation state. Potential of `Ce^(4+)//Ce^(3+)` is +1.74 V. (b) Oxidising properties of `KMnO_(4)` in neutral or faintly alkaline medium. Reaction with iodide ions: `2MnO_(4)^(-)+H_(2)O+I^(-)to2MnO_(2)+2OH^(-)+IO_(3)^(-)` Reaction with thiosulphate : `8MnO_(4)^(-)+3S_(2)O_(3)^(2-)+H_(2)O to8MnO_(2)+6SO_(4)^(2-)+2OH^(-)`