d and f Block Elements — CBSE Class 12 · 2010 · All India Board Question with Solution

a) Complete the following chemical equations:
i) Fe³⁺ + I⁻ →
ii) CrO₄²⁻ + H⁺ →
b) Explain the following:
i) Copper(+1) ion is not stable in an aqueous solution.
ii) With the same d⁴ configuration, Cr(+2) is a reducing agent whereas Mn(+3) is an oxidising agent.
iii) Transition metals in general act as good catalysts.

Solution

(a)(i) Ferric oxidises iodide:

2F e^{3 +} + 2 I^{-} \to 2F e^{2 +} + I_{2}

(ii) Acid converts chromate to dichromate:

2Cr O_{4}^{2 -} + 2 H^{+} \to C r_{2} O_{7}^{2 -} + H_{2} O

(b)(i) Cu

^{+}

disproportionates in water,

2C u^{+} \to C u^{2 +} + Cu

, because the hydration enthalpy of the small, doubly charged Cu

^{2 +}

more than repays the second ionisation enthalpy.
(ii) Cr

^{2 +}

attains the stable d

^{3}

_{2 g}^{3}

) by losing an electron — reducing; Mn

^{3 +}

attains the extra-stable half-filled d

^{5}

by gaining one — oxidising.
(iii) Their variable oxidation states let them shuttle electrons through reactive intermediates, and their surfaces (vacant d-orbitals) adsorb and activate reactants — together providing lower-energy pathways (Fe, Ni, V

_{2}

_{5}

, Pt).

CBSE Class 12 Board · 2010 · All India · Subjective

CBSE Class 12 · 2010 · All India · d and f Block ElementsLong Answer

Solution

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