8.31 How would you account for the following:

(i) Of the d 4 species, Cr2+ is strongly reducing while manganese(III) is strongly oxidising.

(ii) Cobalt(II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised.

(iii) The d 1 configuration is very unstable in ions.

<p><strong>8.31 (i) </strong><strong>Of the d4 species, Cr²⁺ is strongly reducing while manganese (III) is strongly oxidizing: </strong>The +2 oxidation state becomes more stable on moving across a period i.e. the tendency of metals to give electrons becomes more. Therefore, vanadium(II) oxide and chromium(II) oxide are strong reducing agents.</p><p>As if the value of electrode potential is higher i.e. more energy required to withdraw an electron from an isolated atom, more readily it can be reduced and lesser the electrode potential more readily it can be oxidized.</p><p>The electrode potential of Cr³⁺? Cr²⁺is negative so it acts reducing agent or can undergo oxidation which makes it a more stable ion while that of Mn³⁺? Mn²⁺ is positive and it undergoes reduction acts as strong oxidizing agent. Also, Mn³⁺ has an exactly half-filled d- orbital which is highly stable.</p><p><strong>(ii) Cobalt(II) is stable in aqueous solution but in the presence of complexing reagents, it is easily oxidized:&nbsp;</strong>Cobalt gets oxidized from +2 to +3 oxidation state in the presence of complexing reagents.</p><p><strong>(iii) The d¹ configuration is very unstable in ions:</strong>The d¹ electron can be easily lost after the loss of <em>ns </em>electrons. Therefore, the elements having d¹ configuration undergo disproportionation reactions.</p>

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