Question

Answer the following:
Co\(^{2+}\) is easily oxidized to Co\(^{3+}\) in the presence of a strong ligand (At. No. of Co = 27).

Hint:

Strong field ligands can stabilize high oxidation states, like Co\(^{3+}\), by creating a strong ligand field.

Answer 1

To solve the problem, we need to explain why Co\(^{2+}\) is easily oxidized to Co\(^{3+}\) in the presence of a strong ligand.

1. Understanding the Oxidation States of Cobalt:
Cobalt (Co) has two common oxidation states: Co\(^{2+}\) and Co\(^{3+}\). Co\(^{2+}\) has a [Ar] 3d⁷ electron configuration, while Co\(^{3+}\) has a [Ar] 3d⁶ electron configuration. Co\(^{3+}\) is more highly charged, making it more electronegative, and it has a greater tendency to attract electrons from its environment.

2. Role of Strong Ligands:
In coordination chemistry, ligands are molecules or ions that surround a metal ion, forming a coordination complex. Strong ligands are those that form stable complexes with metal ions, leading to significant changes in the metal's electronic structure. A strong ligand is a good electron donor, and it stabilizes the metal ion by interacting strongly with it, often leading to oxidation or reduction of the metal ion.

3. Oxidation of Co\(^{2+}\) to Co\(^{3+}\):
Co\(^{2+}\) is more easily oxidized to Co\(^{3+}\) in the presence of a strong ligand because the ligand stabilizes the Co\(^{3+}\) ion. The presence of a strong ligand such as ammonia (NH₃), cyanide (CN⁻), or ethylenediamine (en) creates a stronger field around the metal, which can lower the energy of the Co\(^{3+}\) ion and make its formation more favorable. In the absence of a strong ligand, Co\(^{2+}\) is relatively stable, but the strong ligand induces an oxidation state change by stabilizing the higher oxidation state (Co\(^{3+}\)).

4. Effect of Ligand Field on Oxidation Potential:
The oxidation potential for Co\(^{2+}\) to Co\(^{3+}\) is relatively low in the absence of a strong ligand. However, the presence of a strong ligand increases the stability of Co\(^{3+}\), thus making the oxidation of Co\(^{2+}\) more favorable. This is because strong field ligands cause a large splitting of the metal's d-orbitals, which stabilizes the higher oxidation state and makes the oxidation process energetically more favorable.

5. Final Answer:
Co\(^{2+}\) is easily oxidized to Co\(^{3+}\) in the presence of a strong ligand because the strong ligand stabilizes the Co\(^{3+}\) ion, making the oxidation of Co\(^{2+}\) to Co\(^{3+}\) more thermodynamically favorable.