Question

Consider the reaction of water with ${{F}_{2}}$ and suggest in terms of oxidation and reduction, which species are oxidized or reduced.

Answer 1

Hint: This reaction leads to the formation of either oxygen or ozone. Consider the difference in electronegativities between fluorine and oxygen and determine whether they will get oxidized or reduced based on that.

Complete step by step solution:
First let us look at the definitions of oxidation and reduction and what they mean in relation to electrons. Oxidation is the loss of electrons, if the oxidation number of a charged species increases after a reaction, it is getting oxidized. Conversely, reduction means the gain of electrons and if the oxidation number is decreasing then the species is getting reduced.
Now, let us determine what will happen when a reaction between water and fluorine takes place and how ozone or oxygen will be formed. We know that fluorine is more electronegative than oxygen, so it will take electrons that were initially with oxygen forming hydrofluoric acid. The two reactions are as follows:
\[\begin{align}
& 2{{F}_{2}}+2{{H}_{2}}O\to {{O}_{2}}+4HF \\
& 3{{F}_{3}}+3{{H}_{2}}O\to {{O}_{3}}+6HF \\
\end{align}\]
In these reactions, we will now check which species are getting oxidized and which are getting reduced. In the first reaction, among the reactants, the oxidation number of fluorine is 0, oxygen in water is -2 and hydrogen in water is +1. On the products side in the first reaction, the oxidation number of oxygen is 0, hydrogen in hydrofluoric acid is +1, and fluorine in hydrofluoric acid is -1. A similar trend is seen in the second reaction as well, but in ozone, since it is a resonating structure, the oxidation number of oxygen is either 0 or +1.
From this we can infer that in both the reactions, the oxidation number of fluorine is decreasing from 0 to -1 and it is getting reduced, while the oxidation number of oxygen is increasing and it is getting oxidized.

So, oxygen acts as a reducing agent while fluorine acts as an oxidizing agent.

Note: An easier way to remember the definition of oxidation and reduction is through the mnemonic OIL RIG here OIL means Oxidation Is Losing (electrons) and RIG means Reduction Is Gaining (electrons).