Question

Explain how $PC{{l}_{5}}$ acts as either an oxidising or reducing agent.

Answer 1

Hint: Determine the oxidation state of Phosphorus in $PC{{l}_{5}}$.
Now think whether $PC{{l}_{5}}$ would be able to either increase or decrease its oxidation state.

Complete step-by-step answer:
Let us first observe the compound $PC{{l}_{5}}$ and obtain some incredibly important data before coming up with a solution to this question.
The highest oxidation state that P can show in $PC{{l}_{5}}$ is +5. In $PCl_5$, phosphorus is in its highest oxidation state (+5).
However, it can decrease its oxidation state to +3 and act as an oxidizing agent.
For instance, the oxidation of Sn with $PC{{l}_{5}}$:
$Sn+2PC{{l}_{5}}\to SnC{{l}_{4}}+2PC{{l}_{3}}$
Therefore, we conclude that $PC{{l}_{5}}$ acts as a fairly effective oxidising agent.
However, due to it already having Phosphorus in its highest oxidation state (+5) and it being incapable of having a higher oxidation state, it is impossible for $PC{{l}_{5}}$ to act as a reducing agent.
Conversely, $PC{{l}_{3}}$ acts an excellent reducing agent but cannot be used as an oxidising agent for pretty much the same reason i.e. Phosphorus being in its lowest oxidation state in this compound.
An example of $PC{{l}_{3}}$ acting as a reducing agent is its reduction of Sulphur Trioxide to Sulphur Dioxide:
$PC{{l}_{3}}+S{{O}_{3}}\to POC{{l}_{3}}+S{{O}_{2}}$
Thus, we have established that while $PC{{l}_{5}}$ can act as an oxidising agent but not as a reducing agent, $PC{{l}_{3}}$ on the other hand is entirely different in nature and can act as a reducing agent but not as an oxidising agent.

NOTE: Do not get confused between the chemical properties of $PC{{l}_{5}}$ and $PC{{l}_{3}}$ while answering this question. Also, it is very essential to be aware of the impact the oxidation state of an element in a compound plays in it acting as either an oxidation or a reduction agent.