Q. How do you determine the oxidizing or reducing agent?
Ans.
A substance that oxidizes another substance is called an oxidizing agent. One that reduces another substance is called a reducing agent.
In a redox reaction, the oxidizing agent gains electrons and is an electron acceptor. The oxidizing agent is therefore reduced in the process.
On the other hand, the reducing agent loses electrons and is an electron donor. The reducing agent is therefore oxidized in the process.
For example, 2Cu + O2 -> 2CuO can be written in ionic form as:
2Cu + O2 -> 2Cu2+ + 2O2-
The two half-reactions for this redox reaction are:
Cu -> Cu2+ + 2e- (oxidation)
O2 + 2e- -> 2O2- (reduction)
Copper is the reducing agent because it is donating electrons to the oxygen. It can be said that the copper is reducing the oxygen by making the oxygen negative. Notice that the copper is itself oxidized in the process.
Oxygen is the oxidizing agent because it is accepting electrons. Notice that the oxygen is itself reduced in the process.