Oxidizing and Reducing Agents

An agent is a causative factor. It influences an element to accept or donate electrons.

An oxidizing agent or oxidant causes an element to lose electrons. Therefore the element undergoes oxidation. The electrons lost by an element are accepted by the oxidizing agent. Hence the oxidizing agent is an electron acceptor.

On the other hand a reducing agent or reductant causes an element to gain electrons. Therefore the element undergoes reduction. The electrons gained by an element are donated by the reducing agent. Hence the reducing agent is an electron donor.

oxidizing agent = electron acceptor reducing agent = electron donor

To understand the terminology let us take an example.

Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

Electronic configuration of Zn with atomic number 30 is 1s2, 2s2, 2p6, 3s2, 3p6, 3d10, 4s2. The fourth shell of zinc requires six electrons to achieve the octet. It is easier for zinc to lose two electrons. Therefore zinc donates two electrons and undergoes oxidation.

The two electrons donated by zinc are taken up by hydrogen and hydrogen undergoes reduction. It can thus be said that zinc has caused the reduction of hydrogen and so zinc is a reducing agent.

Zn atom loses two electrons (oxidation) and is oxidized to Zn2+ ions.

Zn(s) → Zn2+(aq) + 2e-

In the aqueous state HCl dissociates into H+ and Cl- ions

2HCl(aq) → 2H+(aq) + 2Cl-(aq)

Of the two electrons donated by zinc one electron each is accepted by two H+ ions. The two hydrogen ions undergo reduction and form two hydrogen atoms. The two hydrogen atoms combine to form the hydrogen molecule H2. By accepting the electron H+ ion acts as the oxidizing agent. It can thus be said that hydrogen ion has caused the oxidation of zinc and so hydrogen ion is an oxidizing agent.

2H+(aq) + 2e- → H2(g)

Oxidizing agents are reduced and reducing agents are oxidized.