Sum of oxidation state (magnitude) and coordination number of cobalt in Na[Co(bpy) Cl₄] is _________.

Solution

Chemistry ma’am · 3 steps

Two counts here: charges give you +3, and the two nitrogens of bpy give you two donor atoms, not one.

1. Oxidation state. Na⁺ outside the bracket makes the complex ion [Co(bpy)Cl₄]⁻. bpy is a neutral ligand and each Cl⁻ carries -1.

   x + 0 + 4(-1) = -1 ⇒ x = +3

2. Coordination number. bpy (2,2'-bipyridine) binds through both ring nitrogens, so it is bidentate and supplies 2 donor atoms. The four Cl⁻ ions supply 4 more, so the coordination number is 2 + 4 = 6.
3. So. The sum is 3 + 6 = 9.

The common slip: 8. Treating bpy as monodentate gives a coordination number of 5 and a sum of 8. bpy has two donor nitrogens, so it counts as 2.

The idea to keep. Coordination number counts donor atoms, not ligands. Chelating ligands like bpy, en and ox each count twice.

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