CBSE 2025, Set 3

Question

(i) Arrange the following complexes in the increasing order of conductivity of their solution:

$[	ext{Cr(NH}_3)_3	ext{Cl}_3]$,  $[	ext{Cr(NH}_3)_6]	ext{Cl}_3$,  $[	ext{Cr(NH}_3)_5	ext{Cl}]	ext{Cl}_2$

**OR**

(ii) Write two differences between primary and secondary valences in coordination compounds.

Edvaya · Accepted Answer

The correct answer is Subjective. **(i) Increasing order of conductivity:** Conductivity in solution depends on the **number of ions produced** on dissolution: - $[	ext{Cr(NH}_3)_3	ext{Cl}_3]$: All 3 Cl inside coordination sphere — **non-electrolyte**, 0 free ions → lowest conductivity - $[	ext{Cr(NH}_3)_5	ext{Cl}]	ext{Cl}_2$: 2 free Cl$^-$ outside → **2:1 electrolyte** → 3 ions total → intermediate conductivity - $[	ext{Cr(NH}_3)_6]	ext{Cl}_3$: 3 free Cl$^-$ outside → **4:1 electrolyte** → 4 ions total → highest conductivity **Increasing order of conductivity:** $$[	ext{Cr(NH}_3)_3	ext{Cl}_3] < [	ext{Cr(NH}_3)_5	ext{Cl}]	ext{Cl}_2 < [	ext{Cr(NH}_3)_6]	ext{Cl}_3$$ --- **OR (ii) Two differences between primary and secondary valences:** | Primary Valency | Secondary Valency | |---|---| | **Ionisable** — satisfied by negative ions present outside the coordination sphere | **Non-ionisable** — satisfied by ligands (neutral molecules or negative ions) inside the coordination sphere | | Corresponds to the **oxidation state** of the metal | Corresponds to the **coordination number** of the metal |

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Chemistry > Inorganic Chemistry > Coordination Compounds

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