. Complete the following reactions in an aqueous medium


(a) Complete the following reactions in an aqueous medium:

aqueous medium

(b) How would you account for the following:

(i) Metal-metal bonding is more extensive in the 4d and 5d series of transition elements than the 3d series.

(ii) Mn (III) undergoes disproportionation reaction easily.

(iii) Co (II) is easily oxidised in the presence of strong ligands.

OR

(a) Complete the following chemical equations:

equations

(b) Explain the following:

(i) Copper (I) ion is not stable in an aqueous solution.

(ii) With same (d4) configuration Cr (II) is reducing whereas Mn (III) is oxidising.

(iii) Transition metals in general act as good catalysts

 

Best Answer

aqueous medium

(b) (i) The catalytic activity of transition metals and their compounds is attributed to the following reasons:

Because of their variable oxidation states transition metals form unstable intermediate compounds and provide a new path with lower activation for the reaction. In some cases, the transition metal provides a suitable large surface area with free valencies on which reactants are adsorbed. In general in the same group of d block elements, the 4d and 5d transition element has larger size than that of 3d elements. Thus, the valence electrons are less lightly held and hence can form metal-metal bond more frequently.

(ii) Mn3+ is less stable and changes to Mn2+ which is more stable due to half filled d-orbital configuration. That is why, Mn3+ undergoes disproportionation reaction.

(iii) Co (III) has electric configuration 3d, 4s, i.e., it has three unpaired electron. In the presence of strong ligands, two unpaired electrons in 3d subshell pair up and third unpaired electron shift to higher energy subshell from where it can be easily lost and hence oxidised to Co(III).

OR

Fe3+ + I–

(b) (i) In aqueous solution Cu + undergoes disproportionation to form a more stable Cu2+ ion

ionization enthalpy

(ii) Cr2+ is reducing as its configuration changes from d4 to d3 , a more stable half filled t2g configuration while Mn3+ is oxidising as Mn3+ to Mn2+results a more stable half filled d5 configuration.

(iii) The catalytic activity of transition metals and their compounds is attributed to the following reasons: Because of their variable oxidation states transition metals form unstable intermediate compounds and provide a new path with lower activation for the reaction. In some cases, the transition metal provides a suitable large surface area with free valencies on which reactants are adsorbed.

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