Question

Why is Ce\(^{4+}\) in aqueous solution a good oxidising agent?

Hint:

Strong oxidising agents readily get reduced to stable lower oxidation states.

Answer 1

Step 1: Understanding the Oxidation State of Ce⁴⁺.
Cerium (Ce) is a rare earth element that can exist in multiple oxidation states, with +4 and +3 being the most common. In its +4 oxidation state, cerium forms the Ce⁴⁺ ion, which is highly oxidizing. The Ce⁴⁺ ion is particularly strong in accepting electrons, making it a good oxidizing agent.

Step 2: Electronic Configuration of Ce⁴⁺.
The electronic configuration of Ce⁴⁺ is [Xe] 4f⁰, meaning it has no electrons in its 4f orbitals. This makes Ce⁴⁺ highly unstable because it lacks a filled or half-filled stable d- or f-orbital configuration. As a result, it has a strong tendency to gain electrons and reduce to the more stable Ce³⁺ state with an electronic configuration of [Xe] 4f¹.

Step 3: Cerium's Ability to Accept Electrons.
Ce⁴⁺ is a good oxidizing agent because it is readily reduced to Ce³⁺. The reduction of Ce⁴⁺ to Ce³⁺ releases energy, and this makes the Ce⁴⁺ ion eager to accept electrons from other substances. This electron acceptance is the key characteristic of an oxidizing agent.

Step 4: The Role of the 4f Orbitals.
The empty 4f orbitals of Ce⁴⁺ make it highly reactive in aqueous solutions. The energy required to remove an electron from the Ce³⁺ ion is relatively high, so Ce⁴⁺ tends to stay in its +4 state until it interacts with a reducing agent that can donate electrons to stabilize it.

Step 5: Conclusion.
In conclusion, Ce⁴⁺ is a good oxidizing agent in aqueous solution because of its high tendency to accept electrons and reduce to the more stable Ce³⁺ state. The absence of electrons in its 4f orbitals contributes to its strong oxidative nature, making it effective in electron transfer reactions.