Chapter 8.2, Problem 4RQ

Interpretation Introduction

Interpretation :

An oxidation-reduction reaction needs to be explained and how this type of reaction can be identified must be explained.

Concept Introduction :

Oxidation-reduction reactions are also known as redox reaction as in these reactions always oxidation and reduction takes place simultaneously. Oxidation number is the residual charge present on an atom in a compound. Often oxidation number change is used to identify a redox reaction.

Answer to Problem 4RQ

Some of the ways to identify 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.

  $\text{C(s)+}\frac{1}{2}{\text{O}}_{\text{2}}\text{(g)}\to \text{CO(g)}\text{.}$

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

  $\text{Zn(s)+2HCl(aq)}\to {\text{ZnCl}}_2{\text{(aq)+H}}_{\text{2}}\text{(g)}\text{.}$

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

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

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