Chapter 8.3, Problem 3RQ

Interpretation Introduction

Interpretation :

Three ways must be explained to classify oxidation-reduction reactions

Concept Introduction :

Oxidation-reduction reactions are also known as redox reaction as in these reactions always oxidation and reduction takes place simultaneously.

Answer to Problem 3RQ

Three ways to classify oxidation-reduction reactions are given below.

• Checking the change in oxidation number.
• Checking the electron gain or loss.
• Checking the addition or removal of electropositive and electronegative groups or atoms.

Explanation of Solution

When oxidation number of an element in a species is increased then it is an oxidation process. Similarly when oxidation number is decreased then it is reduction process.

  ${\text{C(s)+O}}_{\text{2}}\text{(g)}\to {\text{CO}}_{\text{2}}\text{(g)}\text{.}$

In this reaction C (with oxidation state 0) is oxidized to CO₂ (with oxidation state of C as +4). Oxygen (with oxidation state 0) is reduced to CO₂ (with oxidation state of O as -2).

  ${\text{Zn(s)+H}}_{\text{2}}{\text{SO}}_4\text{(aq)}\to {\text{ZnSO}}_4{\text{(aq)+H}}_{\text{2}}\text{(g)}\text{.}$

In this case Zn is oxidized as electronegative sulfate group is attached with it. Hydrogen is reduced as electronegative group is removed from H₂SO₄.

  ${\text{Zn(s)+Cu}}^{\text{2+}}\text{(aq)}\to {\text{Zn}}^{\text{2+}}\text{(aq)+Cu(s)}\text{.}$

In this reaction Zn is oxidized as electrons are lost. Cu²+ is reduced as it gains electrons.