AgNO₃ vs BaCl₂ Trick 🔥 | Coordination Isomerism

 

❓ Question

Given complex:

$$\text{Co} \cdot 5NH_3 \cdot Cl \cdot SO_4$$

Two isomers A and B:

• A gives white ppt with AgNO₃
• B gives white ppt with BaCl₂

Find the type of isomerism.

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🖼 Question Image

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✍️ Short Concept

Precipitation reactions help identify which ion is outside the coordination sphere.

👉 AgNO₃ detects Cl⁻
👉 BaCl₂ detects SO₄²⁻

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🔷 Step 1 — Understand the Tests 💯

AgNO₃ test:

$$Cl^- \rightarrow AgCl (white ppt)$$

BaCl₂ test:

$$SO_4^{2-} \rightarrow BaSO_4 (white ppt)$$

👉 These ions must be free (outside) to react.

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🔷 Step 2 — Analyze Isomer A

A gives ppt with AgNO₃

So:

$$Cl^- \text{ is outside coordination sphere}$$

Structure:

$$[Co(NH_3)_5SO_4]Cl$$

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🔷 Step 3 — Analyze Isomer B

B gives ppt with BaCl₂

So:

$$SO_4^{2-} \text{ is outside}$$

Structure:

$$[Co(NH_3)_5Cl]SO_4$$

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🔷 Step 4 — Identify Isomerism Type

Here:

• Cl⁻ and SO₄²⁻ exchange positions
• One goes inside coordination sphere
• Other comes outside

This is:

$$\boxed{\text{Ionisation Isomerism}}$$

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✅ Final Answer

$$\boxed{\text{Ionisation Isomerism}}$$

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⭐ Golden JEE Insight

Whenever:

👉 Different reagents give different precipitates

Think:

$$\text{Ionisation Isomerism}$$

👉 Because different ions are free in solution.