JEE Main · 2025 · 24 Jan 2025 · Shift 1 · Coordination Compounds

One mole of the octahedral complex compound

Co (NH_{3})_{5} Cl_{3}

gives 3 moles of ions on dissolution in water. One mole of the same complex reacts with excess of

AgNO_{3}

solution to yield two moles of

AgCl_{(s)}

. The structure of the complex is :

(A) $[Co (NH_{3})_{5} Cl] Cl_{2}$ ✓ Correct
(B) $[Co (NH_{3})_{4} Cl] \cdot Cl_{2} \cdot NH_{3}$
(C) $[Co (NH_{3})_{4} Cl_{2}] Cl . NH_{3}$
(D) $[Co (NH_{3})_{3} Cl_{3}] \cdot 2 NH_{3}$

Answer: (A)

Solution

The complex dissociates into 3 ions in water and reacts with excess

A g N O_{3}

to precipitate only 2 moles of

A g C l

. A chloride ion bonded directly to cobalt inside the coordination sphere is not free in solution and does not precipitate with silver nitrate — only ionic (counter-ion) chloride does.

For

[C o (N H_{3})_{5} C l] C l_{2}

[C o (N H_{3})_{5} C l] C l_{2} \to [C o (N H_{3})_{5} C l]^{2 +} + 2 C l^{-}

— 3 ions in total, matching the first observation.

The two ionic

C l^{-}

ions react with

A g N O_{3}

[C o (N H_{3})_{5} C l] C l_{2} + 2 A g N O_{3} \to [C o (N H_{3})_{5} C l] (N O_{3})_{2} + 2 A g C l ↓

giving exactly 2 moles of

A g C l

, while the coordinated chloride remains bound to cobalt.

The structure of the complex is

[C o (N H_{3})_{5} C l] C l_{2}

JEE Main · 2025 · 24 Jan 2025 · Shift 1 · Single correct option

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JEE Main · 2025 · 24 Jan 2025 · Shift 1 · Coordination Compounds

Solution

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