72

Oxidizing Agent

A substance or a chemical species (atom, ion, etc.) that oxidize other substances but itself gets reduced is called an oxidizing agent. It is one of the reactants that takes or removes electrons from other reactants in a chemical reaction, especially in a redox reaction. The oxidizing agent takes these electrons for itself for fulfilling their requirement of electrons or to get reduced. So, the oxidizing agent itself gets reduced or undergo reduction by taking the electrons from the substance which gets oxidised. For example,

PbS + 4O₃ → PbSO₄ + 4O₂

In the above reaction, ozone is oxidising lead sulphide to lead sulphate and itself gets reduced to oxygen. So, ozone is an oxidizing agent in this reaction. Some common examples of the oxidising agents are halogens, oxygen and hydrogen peroxide.

It is also known as an oxidizer or an oxidant. We can understand an oxidizing agent in different ways as described below;

Electron acceptor: It acts as an electron acceptor as it oxidises which means it takes or gains electrons from another atom that is oxidised by it. In return, an oxidising agent undergoes reduction as it takes electrons.

Atom-transferring substance: It transfers at least one electronegative atom to another substance (molecule or compound) in a chemical reaction. Generally, oxygen is transferred. There are various combustion reactions and organic redox reactions in which the electronegative atom is transferred from one reactant to another reactant. The atom or reactant that receives the oxygen atom is oxidised as oxygen tends to gain electrons to complete its octet.

Factors that affect the oxidizing power of an oxidizing agent

Oxidizing agents generally present in their highest possible oxidation states. So, they tend to gain electrons and thus undergo reduction. The substances (ions, atoms or molecules), which have a strong tendency to gain electrons are considered good oxidizers. So, the more the oxidation state (attraction for electrons) the more is the oxidizing power of a substance.

For example, fluorine is the most electronegative element and thus strongly attracts electrons. So, it is believed to be the strongest oxidizing agent among all the elements.

Similarly, some metals like asbestos and quartz when exposed to diatomic fluorine (F2) burst into flames due to the high oxidizing power of diatomic fluorine. The other strong oxidizing agents (good electron acceptors) include diatomic oxygen (O₂), diatomic chlorine (Cl₂),) and ozone (O₃),).

Some compounds that have a large oxidation state or number also act as good oxidising agents. For example some ions such as permanganate ion, the chromate ion, the dichromate ion. Similar some acids are good oxidizing agents such as nitric acid, perchloric acid, and sulphuric acid.

Furthermore, the more is the electronegativity more is the oxidation state and thus more is the ability of an element to oxidise other substances.

Common examples of oxidizing agents

Halogens:

The elements of group 17 of the periodic table are known as halogens. Their tendency to gain electrons is very high due to their high electronegativities. For example halogens like bromine, iodine and fluorine are good oxidising agents.

Oxygen:

Oxygen belongs to chalcogens (ore-forming) group 16 of the periodic table. It is a highly reactive non-metal with good oxidizing potential. So, it easily forms metal oxides by oxidising metals, e.g. magnesium oxide (MgO).

Hydrogen Peroxide:

Hydrogen peroxide is a chemical compound, which appears as a colourless liquid. It is a weak oxidising agent and commonly used as a disinfectant and bleaching powder.

Uses or applications of oxidizing agents

There are lots of commercial and industrial uses of oxidizing agents some of which are listed below;

• Bleaching of fabrics
• Purification of water
• Combustion of fuel
• For storing energy in batteries
• Vulcanization of rubber

Reducing Agent

A substance that reduces the other substance and in return gets oxidised by losing electrons is called a reducing agent.

Zn + CuSO₄ (aq) → ZnSO₄ (aq) + Cu

For example in the above reaction zinc is a reducing agent as the electrons lost by Zn are gained by Cu. So, Zn acts as a reducing agent for CuSO₄. Now, we know that a reducing agent oxidises itself. In this case, Zn is oxidised to Zn²⁺ and forms ZnSO4. The Cu has the tendency to take two electrons and Zn loses these two electrons, so Zn acts as a reducing agent for copper. Copper is getting electrons from Zn so copper is oxidising Zn.

Similarly, in the below reaction, the ferric oxide acts as an oxidising agent as it transfers the oxygen atom to the carbon monoxide molecule.

Fe₂O₃ + 3CO → 2Fe + 3CO₂

Furthermore, in a redox reaction, one of the reactants act as a reducing agent and reduces the other reactant by giving its electrons. The reducing agent itself gets oxidised which means its oxidation state or number increases.

Characteristics of Reducing agents

• They have a tendency to give or donate electrons. The metals in the s-block due to their high tendency to lose electrons are considered good reducing agents.
• They get oxidised as they lose electrons.
• They have low electronegativity.
• Strong reducing agents tend to be weak oxidizing agents as they cannot gain electrons easily such as sodium is a strong reducing agent but a weak oxidizing agent.

Examples of reducing agents

Lithium: It is an element with atomic number 3. It belongs to the alkali metal group of the periodic table. It acts as a strong reducing agent when placed in solutions.

Iodides: The iodide salts are considered mild reducing agents. They react with oxygen to produce iodine.

Reducing sugars: They also act as reducing agents. This is because they have a free ketone group or a free aldehyde group. For example, monosaccharides, disaccharides, polysaccharides and oligosaccharides are considered reducing sugars.

Metals: Metals of groups IA and IIA.

Non-metals: Some non-metals like Carbon (C), Sulphur (S), Phosphorus (P) and Hydrogen (H).

Hydrogen halides: Such as HI, HBr, and HCl are good reducing agents.

Metal hydrides: They include lithium hydride (LiH) and calcium hydride (CaH₂).

Organic acids: Some organic acids like HCOOH (formic acid) and (COOH) ₂ (oxalic acid).

Difference between oxidising agent and reducing agent

Oxidizing Agent	Reducing Agent
It oxidizes other substances but itself gets reduced.	It reduces other substances but itself gets oxidized.
It gains electrons from other reactants in a redox reaction.	It gives or donates electrons to other reactants in a redox reaction.
It loses oxygen in a reaction.	It gains oxygen in a reaction.
It gains hydrogen in a reaction.	It loses hydrogen in a reaction.
It is an electron acceptor.	It is an electron donor.
It is usually a non-metal or a positive ion.	It is generally a metal or a negative ion.
The strongest oxidizing agent is fluorine.	Lithium when present in a solution is the strongest oxidizing agent.
Its oxidation state or number decreases in a reaction.	Its oxidation state or number increases in a reaction.
Generally, all non-metals act as oxidizing agents.	All metals, hydrides, etc., act as reducing agents.
Their atoms have high electronegativity.	Their atoms have low electronegativity.
Examples include halogens, potassium nitrate.	Examples include earth metals, oxalic acid, formic acid, etc.

---