Q16 of 26 Page 1

(a) For the complex [CoF6]3-, write the hybridization type, magnetic character and spin nature of the complex. (Atomic no. of Co = 27)

(b) Why is the complex [Co(en)3]3+ more stable than [CoF6]3-?


(a) Electronic configuration of Co : [Ar] 3d74s2

Electronic configuration of Co3+ : [Ar] 3d64s0


Cobalt is in +3 oxidation state since there is a net negative charge of -3 on the complex and fluoride carries a charge of -1. So -1 x6 is -6.


Fluorine is a weak field ligand so pairing up of electrons of cobalt does not occur. So forms a high spin, outer d-complex.


3d64s0



As there are unpaired electrons the complex will be paramagnetic.


Hybridization is sp3d2 (outer d)



(b) Ethylenediamine(en) is a bidentate ligand while fluoride is a monodentate ligand. Polydentate ligands show chelating effect which leads to stability of the complex. Since complex [Co(en)3]3+ shows chelating effect it is more stable than [CoF6]3-.


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(a) Indicate the principle behind the method for the refining of zinc.

(b) Account for the following:


(i) It is advantageous to roast sulphide ore to oxide before reduction.


(ii) Zinc oxide can be reduced to metal by heating with carbon but not Cr2O3.


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Account for the following:

(a) Inter-halogen compounds are more reactive than pure halogens.


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(a) How do you convert the following?

(i) Prop-1-ene to propan-2-ol.


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Write the reactions involved in the following:

(a) Aldol condensation


(b) Cannizzaro’s reaction


(c) Rosenmund reaction