With the help of various examples of redox reactions mentioned in this article, students will find it easy to understand the meaning of redox reactions and the chemical processes occurring in them.
The concept of oxidation and reduction are the basics of elementary chemistry classes in schools and colleges. When students are introduced to chemical reactions, they are made to understand the concept of oxidation and reduction that help them to interpret the change in chemical equations and the formation of end products or compounds.
What is a Redox Reaction?
The word ‘redox’ is the acronym for reduction-oxidation that occurs in a certain chemical reaction. Put more simply, these reactions are those sets of chemical equations in which the oxidation number of the atoms involved in the chemical reaction changes when the reaction occurs. This definition introduces us to another fundamental concept in chemistry that is of crucial importance, the oxidation number. Let us define it.
Oxidation number is exactly similar to the valency of an atom but carries a sign with it. This sign expresses the nature of charge on the corresponding species when it is formed from a neutral atom. Let us understand this through an example. The oxidation number of chlorine in hydrochloric acid (HCl) is -1, in Chloric acid (HClO3) is +5, and in perchloric acid (HClO4) it is +7.
How do we calculate oxidation number? Well, for calculating oxidation number, one has to consider various oxidation states of all atoms in a molecule and then equate the sum of all of them to the net charge on the molecule. There are various rules for finding oxidation number of an atom in a molecule however, here we will just see how to find oxidation number of Cl in HClO3.
Oxidation number of H = +1
Oxidation number of Cl = Z (let us suppose)
Oxidation number of O = -2
+1 + Z + 3 (-2) = 0 (since net charge on HClO3 = 0),
+1 + Z + (-6) = 0
Z = +5
So on a general note, oxidation generally involves any of the following changes:
|Loss of electrons
Loss of hydrogen atoms
Gain of oxygen
Increase in oxidation state
Similarly, reduction is said to occur when any of the following changes occur:
|Gain of electrons
Gain of hydrogen atoms
Loss of oxygen atoms
Decrease in oxidation state
Here is one of the simplest examples of these reactions, that will help you to get a better idea of this concept.
Formation of Hydrogen Fluoride
Reaction: H2 + F2 = 2HF
Substance oxidized: Hydrogen
Substance reduced: Fluorine
Oxidation Reaction: H2 → 2H+ + 2e–
Reduction Reaction: F2 + 2e– → 2F–
In the first reaction, hydrogen oxidizes by increasing its oxidation number from 0 to +1 while in the second reaction, fluorine is reduced by decreasing its oxidation number from 0 to -1. Eventually, net charge on the molecules formed is zero as number of electrons gained during oxidation are consumed during reduction process. Finally, the equation turns out to be,
H2 → 2H+ + 2e– + F2 + 2e– → 2F– = H2 + F2 = 2H+ + 2F–
H2 + F2 → 2H+ + 2F– → 2HF
In the examples given below, only the complete reactions have been mentioned instead of the half cell reactions.
Reaction between Fe(II) and CuSO4 solution
Fe + CuSO4 + → FeSO4 + Cu (Fe oxidized, Cu reduced)
Oxidation of Fe(II) to Fe(III) by hydrogen peroxide and an acid: 2 Fe2+ + H2O2 + 2 H+ → 2 Fe3+ + 2 H2O
Glucose oxidation to carbon dioxide: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
Reaction between Potassium Permanganate and Sodium Sulfite: 2 KmnO4 + 3 Na2SO3 + H2O → 2 MnO2 + 3 Na2SO4 + 2 KOH
Reaction of an acid and a base: 3 CuS + 8 HNO3 → 3 CuSO4 + 8 NO (g) + 4 H2O
In chemistry and biology, there are innumerable examples in which the process of oxidation and reduction occur. Redox reactions, in fact, play a crucial role in biochemical reactions, industrial processes, and other chemical works. Transfer of cells and glucose oxidation in the body are also classic examples of these type of reactions. Reactions in chemical factories, electrochemical reactions, obtaining metals from their ores, and preparation of certain fertilizers are all examples of redox reactions.