1 mol of an octahedral metal complex with formula MCl₃ . 2L on reaction with excess of AgNO₃ gives 1 mol of AgCl. The denticity of Ligand L is ____________. (Integer answer)

Solution

Chemistry ma’am · 4 steps

The AgCl tells you which chlorides are outside the bracket; the rest share the six sites with L.

1. Free chloride. Only chloride ions outside the coordination sphere react with AgNO₃. Coordinated chlorides are held by the metal and do not precipitate.
2. Count the chlorides. 1 mol of complex gives 1 mol of AgCl, so 1 Cl⁻ is outside. The other 2 chlorides are bonded to the metal, so the complex is [MCl₂L₂]Cl.
3. Fill six sites. An octahedral complex has coordination number 6. The 2 chlorides take 2 sites, which leaves 4 sites for the 2 L ligands.

   2 + 2d = 6 ⇒ d = 2

4. So. Each L binds through two donor atoms, so the denticity of L is 2 (bidentate, like en).

The common slip: 4. Giving all 4 remaining sites to a single L gives 4, but there are two L ligands sharing those 4 sites.

The idea to keep. Moles of AgCl count only the ionisable chlorides. Put the rest inside the bracket, then share the remaining coordination sites among the other ligands.

Answer from the NTA final answer key. Solution by PrepWiser.