Question

How does water act both as an oxidising agent and reducing agent? Give examples.

Answer 1

As we know that an oxidising agent is the one which has the capacity to oxidise another compound and itself gets reduced whereas a reducing agent is the one which has the capability to reduce another compound and itself gets oxidised.

Complete solution:
As we know that in terms of redox reaction, water can act as an acid as well as a base and thus it is amphoteric in nature. In the presence of a strong electron donor which is basically a reducing agent, water can serve as an oxidising agent in this case.
Also we are aware that in the presence of a strong electron acceptor which is generally a strong oxidising agent, water can serve as a reducing agent.
We can take an example to explain the reducing nature of water such as a reaction where water acts as a reducing agent in the presence of fluorine which is acting as an oxidising agent in the reaction thereby converting the water into ozone or oxygen. We can show this reaction as:
$2{F_2} + 2{H_2}O \to 4HF + {O_2}$
And, for describing water as an oxidising agent we can take an example of reaction of water with lithium where lithium behaves as a reducing agent thereby reducing water into hydrogen. So, we can show this reaction as below:
$2Li + 2{H_2}O \to 4LiOH + {H_2}$

Therefore, we can say that water behaves as both a reducing as well as an oxidising agent in the course of a reaction.

Note: Remember that water is actually weak while behaving as an oxidising agent as well as a reducing agent, so its behaviour usually depends on the substance which is present for the reaction with water. Also, water usually makes a good solvent for redox reactions as it can behave as a weak base as well as a weak acid .