Ionisation Isomerism Using Precipitation Tests

 

❓ Concept Question

How do we identify ionisation isomerism using precipitation tests in coordination compounds?

---

🖼 Concept Image

---

✍️ Short Concept

Different reagents detect specific free ions in solution.

👉 That tells us which ion is outside the coordination sphere.

---

🔷 Step 1 — Given Complex Nature 💯

$$\text{Co}\cdot 5N{H}_3\cdot Cl\cdot S{O}_4$$

Octahedral complex:

👉 Coordination number = 6

So:

• 5 NH₃ + 1 anion inside
• 1 anion outside

---

🔷 Step 2 — AgNO₃ Test

AgNO₃ detects:

$$Cl^- \rightarrow AgCl \ (\text{white ppt})$$

👉 If white ppt forms → Cl⁻ is free (outside)

---

🔷 Step 3 — BaCl₂ Test

BaCl₂ detects:

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

👉 If white ppt forms → SO₄²⁻ is outside

---

🔷 Step 4 — What Changed?

Isomer A:

• Cl⁻ outside
• SO₄²⁻ inside

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

Isomer B:

• SO₄²⁻ outside
• Cl⁻ inside

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

👉 Inner ↔ outer ion exchange

---

🔷 Step 5 — Golden Concept

When:

$$\text{Counter ion} \leftrightarrow \text{Coordinated ion}$$

swap happens →

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

---

✅ Final Takeaway

✔ Same composition
✔ Different ions released in solution

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

---

⭐ Golden JEE Insight

If different reagents give different precipitates:

👉 Immediately think:

$$\text{Ionisation Isomerism}$$