Question

Tell which of the following are oxidation–reduction reactions. For those that are, identify the oxidizing agent, the reducing agent, the substance being oxidized, and the substance being reduced.

$\begin{array}{l}\mathbf{a}.{\mathbf{CH}}_4\left(g\right)\text{+}\mathbf{2}{\mathbf{O}}_2\left(g\right)\to {\mathbf{CO}}_2\left(g\right)\text{+}\mathbf{2}{\mathbf{H}}_2\mathbf{O}\left(g\right)\\ \mathbf{b}.\mathbf{Zn}\left(s\right)\text{+}\mathbf{2}\mathbf{HCl}\left(\mathrm{aq}\right)\to {\mathbf{ZnCl}}_2\left(\mathrm{aq}\right)\text{+}{\mathbf{H}}_2\left(g\right)\\ \mathbf{c}.{\mathbf{Cr}}_2{{\mathbf{O}}_7}^{\mathbf{2}-}\left(\mathrm{aq}\right)\text{+}\mathbf{2}{\mathbf{OH}}^{-}\left(\mathrm{aq}\right)\to \mathbf{2}{{\mathbf{CrO}}_4}^{\mathbf{2}-}\left(\mathrm{aq}\right)\text{+}{\mathbf{H}}_2\mathbf{O}\left(l\right)\\ \mathbf{d}.{\mathbf{O}}_3\left(g\right)\text{+}\mathbf{NO}\left(g\right)\to {\mathbf{O}}_2\left(g\right)\text{+}{\mathbf{NO}}_2\left(g\right)\\ \mathbf{e}.\mathbf{2}{\mathbf{H}}_2{\mathbf{O}}_2\left(l\right)\to \mathbf{2}{\mathbf{H}}_2\mathbf{O}\left(l\right)\text{+}{\mathbf{O}}_2\left(g\right)\\ \mathbf{f}.\mathbf{2}\mathbf{CuCl}\left(\mathrm{aq}\right)\to {\mathbf{CuCl}}_2\left(\mathrm{aq}\right)\text{+}\mathbf{Cu}\left(s\right)\\ \mathbf{g}.\mathbf{HCl}\left(g\right)\text{+}{\mathbf{NH}}_3\left(g\right)\to {\mathbf{NH}}_4\mathbf{Cl}\left(s\right)\\ \mathbf{h}.{\mathbf{SiCl}}_4\left(l\right)\text{+}\mathbf{2}{\mathbf{H}}_2\mathbf{O}\left(l\right)\to \mathbf{4}\mathbf{HCl}\left(\mathrm{aq}\right)\text{+}{\mathbf{SiO}}_2\left(s\right)\\ \mathbf{i}.{\mathbf{SiCl}}_4\left(l\right)\text{+}\mathbf{2}\mathbf{Mg}\left(s\right)\to \mathbf{2}{\mathbf{MgCl}}_2\left(s\right)+\mathbf{Si}\left(s\right)\end{array}$

Short answer

Among the given chemical reactions, b), d), e), f), i) are the redox reactions.

Step-by-step solution

Introduction

In the oxidation-reduction reactions, the mutual gaining and losing of electrons take place between the reactants simultaneously. These reactions are also called redox reactions.

Oxidizing agent undergoes reduction (gains electrons).

Reducing agent undergoes oxidation (loses electrons).

Subpart a)

The given reaction is not a redox reaction. In this reaction, only reduction takes place.

The oxidation state of oxygen changes from 0 to –2. So oxygen undergoes reduction. The oxidation state of other atoms remains unchanged.

Subpart b)

The given reaction is a redox reaction. In this reaction, both oxidation and reduction reactions occur simultaneously.

Zn - oxidation state changes from 0 to +2.

H - oxidation state changes from +1 to 0.

Hence, Zn is the reducing agent which undergoes oxidation.

HCl is the oxidizing agent and hydrogen undergoes reduction.

Subpart c)

The given reaction is not a redox reaction. The oxidation states of the atoms remain unchanged

Subpart d)

The given reaction is a redox reaction.

NO is the reducing agent and N-atom undergoes oxidation.

Ozone is the oxidizing agent and O-atom in ozone undergoes reduction.

Subpart e)

The given reaction is a redox reaction.

Oxygen atom undergoes both oxidation and reduction.

Subpart f)

The given reaction is a redox reaction.

Copper atom undergoes both oxidation and reduction.

Subpart g)

The given reaction is not a redox reaction. The oxidation states of the atoms remain unchanged

Subpart h)

The given reaction is not a redox reaction. The oxidation states of the atoms remain unchanged

Subpart i)

The given reaction is a redox reaction.

The Si-atom undergoes reduction. Thus, $SiC{l}_4$ is the oxidizing agent.

Mg-atom undergoes oxidation. Hence, Mg is the reducing agent.