Class 11th science chemistry (Redox reaction)

Redox reaction is the combination of both oxidation and reduction reactions. When redox reaction takes place, both oxidation and reduction reactions also occur simultaneously.

What is a Redox Reaction?

Redox is a term used for the oxidation-reduction reaction. Redox reaction is a chemical reaction where a change in the oxidation state of atoms occurs. It involves electron transfer i.e if one chemical species gains electrons, then another chemical species gives or loses electrons. The species from which the electron is lost is said to be oxidized whereas the species to which the electron is added is said to be reduced. Example zinc displaces copper in an aqueous solution called copper sulfate.

Redox reactions can be classified into four different categories:

• Combination reaction
• Decomposition reaction
• Displacement reaction
• Disproportionation reaction

Oxidizing And Reducing Agents

The role of an oxidizing agent (Oxidant) in a chemical reaction is to gain electrons. They are highly electronegative. Once they gain electrons these substances are reduced. An oxidant is also known as an electron acceptor. Example nitric acid, halogen, etc.

The role of a reducing agent (Reductant) in a chemical reaction is to lose electrons. Once they lose electrons these substances are oxidized. A reductant is also known as an electron donor. Example sulfite compounds, earth metals, etc.

Oxidizing agents refer to the reactants in oxidation-reduction reactions involving a transfer of electrons between the reacting species in order to form a product. There exist various processes that involve oxidizing agents, including chemical redox reactions such as rusting/corrosion and combustion.

The species known as oxidizing agents are also referred to as oxidizers or oxidants. They possess a tendency to gain electrons and get reduced in a chemical reaction. This is the reason why they’re also identified as electron acceptors.

• Oxidizing agents are normally in their highest possible oxidation states and therefore, they strongly tend to gain electrons and undergo reduction. Some common examples of oxidizing agents include halogens such and chlorine and fluorine, nitric acid, and potassium nitrate.
• From the concepts established above, it can be understood that Ions, Atoms, and molecules which tend to have a strong affinity towards electrons are considered to be good oxidizers or oxidizing agents.
• Elemental fluorine is said to be the strongest elemental oxidizing agent. This is perhaps due to the fact that fluorine is the most electronegative element in the modern periodic table, and therefore exerts the strongest attractive force on electrons amongst all the elements.
• In fact, the oxidizing power of diatomic fluorine (F2) is strong enough to cause metals such as asbestos and quartz, and even molecules such as water, to burst into flames when exposed to it.
• A few other examples of elemental oxidizing agents include diatomic oxygen (O2), diatomic chlorine (Cl2), and ozone (O3). These oxidizers are the elemental forms of the second and the third most electronegative elements (oxygen and chlorine respectively), making them good electron acceptors.
• Some compounds that exhibit large oxidation states can also be considered as good oxidizing agents. Ionic examples include the permanganate ion, the chromate ion, and the dichromate ion. Acidic examples of good oxidizers include nitric acid, perchloric acid, and sulfuric acid. The electronegativity of the molecules increases with the increase in the oxidation states of the atoms, increasing their ability to oxidize other substances.

A few examples of good oxidizing agents are listed below along with a brief description of their properties.

• Halogens- The group 17 elements of the periodic table are collectively referred to as the Halogens. They are said to have a strong ability to gain electrons, attributed to their high electronegativities when compared to elements from other groups. This implies that they have the ability to easily attract electrons towards their respective nuclei. Examples of the halogens that are good oxidizing agents include iodine, bromine, chlorine, and fluorine. Fluorine is said to be the strongest elemental oxidizing agent due to its highest electronegativity, as discussed earlier.
• Oxygen– Oxygen is the element corresponding to the atomic number 8 and is denoted by the symbol ‘O’. It belongs to the chalcogen group of the periodic table and is a highly reactive non- metal with good oxidizing properties. In general, metals tend to form metal oxides by reacting with the atmospheric oxygen, due to the strong oxidizing power of oxygen. Oxygen is observed to be a part of a majority of combustion reactions.
• Hydrogen peroxide– Hydrogen peroxide is the chemical compound having formula H2O2. It appears to the human eye as a colorless liquid which has a greater viscosity than water. Hydrogen peroxide is the simplest compound having a peroxide functional group with an oxygen-oxygen single bond. It finds its uses as a weak oxidizing agent, disinfectant, and a bleaching agent.

Many other oxidizing agents are commonly used industrially as well as in the day to day lives of humans. Examples include household bleach (NaClO), Potassium Nitrate (KNO3), and Sulfuric acid (H2SO4).

Applications of Oxidizing Agents

Oxidizing agents have numerous commercial and industrial applications. A few of these applications are listed below.

• Bleaching of fabrics.
• Purification of water.
• Combustion of fuel involves the use of an oxidizing agent.
• Storage of energy in batteries.
• Vulcanization of rubber (increasing the strength and the elasticity of rubber).
• Oxidizing agents are also vital to many biological processes such as metabolism and photosynthesis.

Reducing Agents- Definition and Meaning

A reducing agent is one of the reactants of an oxidation-reduction reactions which reduces the other reactant by giving out electrons to the reactant. If the reducing agent does not passes electrons to other substance in an reaction, then the reduction process cannot occur.

Definition– “The substance which loses electrons to the other substance and gets oxidized to the higher valency state is known as reducing agent.”

The reducing agents give away electrons. The metals of the s-block in the periodic table are said to be good reducing agents. These agents have an opposite effect to measuring the agents which tend to strengthen. The reducing agent after losing electrons gets oxidized and also causes the opposite reactant to get reduced by supplying electrons. All the good reducing agents have the atoms which have low electronegativity and a good ability of atom or a molecule to attract the bonding electrons and the species having very small ionization energies. These usually serve as the good reducing agents.

All the oxidation and reduction reactions involves the transfer of electrons. When some substance is oxidized, it is said to lose electrons and the substance which receives electrons is said to be reduced. If the substance has strong tendency to lose electrons, then it is said to be strong reducing agent as it will reduce the other substances by giving electrons.

The more strong the reducing agent, the more weaker is the corresponding oxidizing agent. Fluorine gas is known to be a strong oxidizing agent and whereas F- is said to be a weak reducing agent. We also know that – the more weaker an acid then more stronger is the conjugate base. In a similar way, the more weaker the oxidizing agent then the more strong is the corresponding reducing agent as shown in the figure below.

Reducing Agent- Examples

Some of the common reducing agents includes metals such as Na, Fe, Zn, Al and non-metals such as C, S, H2. Some of the compounds and also the Hydracids such as HCl, HI, HBr, H2S behave as good reducing agents. A brief explanation over some of the reducing agents are given below-

• Lithium– lithium is a chemical element with atomic number 3 and a symbol Li. It appears as a soft and silvery white metal and belongs to the alkali metal group of the periodic table. It is said to be a strong reducing agent when placed in solutions.
• Iodides– The salts of Iodides are said to be mild reducing agents. They react with oxygen to give out iodine. These also possess various antioxidant properties.
• Reducing sugars– Reducing sugars are those which behave in a similar as that of the reducing agents because of the free ketone group or a free aldehyde group present. All monosaccharides along with disaccharides, polysaccharides, oligosaccharides are said to be reducing sugars.

Some of the other compounds of reducing agents includes Carbon, Carbon monoxide, Ascorbic acid, sulphur dioxide , Hydrogen, Oxalic acid, Phosphites, phosphorous acid, hypophosphites, etc.