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Oxidation Reduction Reaction

Oxidizing and Reducing Agent

Oxidizing and reducing agents are always going hand to hand in oxidation-reduction or redox reactions. Hence in learning chemistry, the oxidation-reduction process, one element, or molecule oxidizing agent, another element or molecule must be simultaneously reducing agent. According to the electronic concept, the oxidizing agent gains electrons and reduced to the lower oxidation number or state but reducing agent losses electrons and oxidized to the higher oxidation state or number. For example, the formation of crystalline solid MgO. Hence each magnesium atom loses two electrons to form Mg+2-ion and neutral oxygen atom gains two electrons to form O-2-ion. These two ions bonding to form a closed packed type crystal lattice. Therefore, oxidation-reduction reaction going hand to hand for the formation of MgO.

Classical Concept of Oxidation Reduction

Oxidation of the reducing agent and reduction of oxidizing agent

Classically oxidation has defined as the combination of oxygen or electronegative element with another element or compound or the removal of hydrogen or electropositive element from a chemical compound. In the same way, the reduction has defined as the combination of hydrogen or electropositive element with another element or compound or the removal of oxygen or electronegative element from a chemical compound.

2Mg + O2 ⇆ 2MgO

On the above reaction magnesium metal, burns in oxygen to produce magnesium oxide with the addition of oxygen is called oxidation.

Electronic Concept of Oxidation Reduction

The electronic structure of elements gives the quantitative relations between classical and electronic concept oxidation and reduction reaction.

2Mg → 2Mg+2 + 4e
O2 + 4e → 2O-2

In the above balancing equations, oxygen has to lead the removal of two valence orbital electron particles from magnesium metal to form stable zerovalent Mg+2 ion. On the other hand, the lost electron have found new homes in oxygen to form O-2 ion. Therefore, the classical definition of oxidation-reduction has an intimate connection with the electronics concept.

Examples of Oxidizing Agent

Combination of Oxygen examples

  • All the hydrocarbon like methane, ethane, propane, etc readily burns in excess air or oxygen to form carbon dioxide and water but controlled oxidation gives various products. For example, oxidation in the presence of boric acid produces a mixture of secondary alcohols. Oxidizing reagents such as potassium permanganate really oxidizes tertiary hydrogen atom to form the hydroxyl group.

CH3-CH3 + 3[O] → 2CO2 + 3H2O
(CH3)3CH + [O] → (CH3)3COH

Combination of electronegative element

Group-17 elements in periodic table stable on negative oxidation state and oxidation power decreases from fluorine to iodine. Therefore, the electronegative elements chlorine oxidizes the colorless FeCl2 solution to red FeCl3.

2FeCl2 + Cl2 ⇆ 2FeCl3

Removal of hydrogen examples

  • When MnO2 heating with concentrated hydrochloric acid, it produces greenish-red chlorine gas. Therefore, hydrogen can be removed from hydrochloric acid to form chlorine gas.

4HCl + MnO2 ⇆ MnCl2 + Cl2 + H2O

  • Oxidation of hydrogen sulfide to sulfur in the presence of nitric acid. In this reaction, hydrogen can remove from the hydrogen sulfide molecule.

H2S + 2HNO3 ⇆ S↓ + 2NO2 + 2H2O

Removal of electro-positive elements

Hydrogen peroxide oxidizes hexacyanoferrate (II) to hexacyanoferrate (III) in presence of acid solution.

2[Fe(CN)6]4- + H2O2 +2H+ → 2[Fe(CN)6]4- + 2H2O

Example of Reducing Agent

Addition of hydrogen examples

  • Alkenes are rapidly added hydrogen atom or hydrogenated under pressure in the presence of the catalyst like platinum or palladium surface.

C2H4 + H2 → C2H6

  • Reduction of monocarboxylic acid in organic chemistry. The deduction of monocarboxylic acid depends on the nature of reducing agents, heat, and catalyst used. Therefore, monocarboxylic acid heating with hydrogen iodide and red phosphorus under pressure or with hydrogen under pressure at specific heat in the presence of nickel catalyst produces an alkane.

RCO2H + 3H2 → RCH3 + 2H2O

Addition of electro-positive elements examples

Hydrogen peroxide reduces hexacyanoferrate (III) to hexacyanoferrate (II) in the base or high pH solution.

2K3[Fe(CN)6] + 2KOH + H2O2 ⇆ 2K4[Fe(CN)6] + 2H2O + O2

Hence in the above reaction potassium ferricyanide combine with electro-positive element potassium to produce potassium ferrocyanide.

Removal of oxygen oxidizing agent

When hydrogen passes through heated black color CuO, oxygen removes from CuO to form red copper.

CuO + H2 ⇆ Cu +H2O

Removal of electro-negative elements

When SO2 passes through a red ferric sulfate solution, it turns into a greenish ferrous sulfate and sulfuric acid.

Fe2(SO4)3 + 2SO2 + H2O ⇆ 2FeSO4 + 2H2SO4

In the above reaction, electronegative sulfate removes form ferric sulfate. Therefore, ferric sulfate reduced to form ferrous sulfate.