Chapter 20, Problem 80A

(a)

Interpretation Introduction

Interpretation: The half-reactions are to be balanced. The anions that act as an oxidizing or reducing agent is to be identified.

Concept Introduction: An equation illustrating just the reduction or just oxidation that occurs in a redox reaction is called a half-reaction. The oxidation and reduction half-reactions are written individually in the half-reaction approach before being compared to create a balanced redox equation.

Answer to Problem 80A

  ${\text{Cr}}_{\text{2}}{\text{O}}_7^{2-}$ acts as an oxidizing agent.

Explanation of Solution

An element is oxidized and acts as a reducing agent when its oxidation number rises.

The oxidizing agent is the element whose oxidation number decreases.

Consider the given half-reaction.

  ${\text{Cr}}_{\text{2}}{\text{O}}_7^{2-}\left(aq\right)\to {\text{Cr}}^{\text{3+}}\left(aq\right)$

The above equation in balanced form is given as follows:

  $\stackrel{+6}{{\text{Cr}}_{\text{2}}}{\text{O}}_7^{2-}\left(aq\right)+14{\text{H}}^{+}+6e^{-}\to 2{\text{Cr}}^{\text{3+}}\left(aq\right)+7{\text{H}}_{\text{2}}\text{O}\left(l\right)$

There is change in oxidation number of chromium.

The oxidation number of chromium is changed from $+6$ to $+3$ . So, chromium is reduced.

  ${\text{Cr}}_{\text{2}}{\text{O}}_7^{2-}$ anion acts as an oxidizing agent in the reaction.

(b)

Interpretation Introduction

Interpretation: The half-reactions are to be balanced. The anions that act as an oxidizing or reducing agent is to be identified.

Concept Introduction: An equation illustrating just the reduction or just oxidation that occurs in a redox reaction is called a half-reaction. The oxidation and reduction half-reactions are written individually in the half-reaction approach before being compared to create a balanced redox equation.

Answer to Problem 80A

  ${\text{S}}_{\text{2}}{\text{O}}_3^{2-}$ acts as a reducing agent.

Explanation of Solution

An element is oxidized and acts as a reducing agent when its oxidation number rises.

The oxidizing agent is the element whose oxidation number decreases.

Consider the given half-reaction.

  ${\text{S}}_{\text{2}}{\text{O}}_3^{2-}\left(aq\right)\to {\text{SO}}_4^{2-}\left(aq\right)$

The above equation in balanced form is given as follows:

  $\stackrel{+4}{{\text{S}}_{\text{2}}}{\text{O}}_3^{2-}\left(aq\right)+5{\text{H}}_2\text{O}\to 2\stackrel{+6}{\text{S}}{\text{O}}_4^{2-}\left(aq\right)+10{\text{H}}^{+}{\text{+8e}}^{-}$

There is change in oxidation number of sulfur.

The oxidation number of sulfur is changed from $+4$ to $+6$ . So, sulfur is reduced.

  ${\text{S}}_{\text{2}}{\text{O}}_3^{2-}$ acts as a reducing agent in the reaction.

(c)

Interpretation Introduction

Interpretation: The half-reactions are to be balanced. The anions that act as an oxidizing or reducing agent is to be identified.

Concept Introduction: An equation illustrating just the reduction or just oxidation that occurs in a redox reaction is called a half-reaction. The oxidation and reduction half-reactions are written individually in the half-reaction approach before being compared to create a balanced redox equation.

Answer to Problem 80A

  ${\text{CrO}}_4^{2-}$ acts as an oxidizing agent.

Explanation of Solution

An element is oxidized and acts as a reducing agent when its oxidation number rises.

The oxidizing agent is the element whose oxidation number decreases.

Consider the given half-reaction.

  ${\text{CrO}}_4^{2-}\left(aq\right)\to \text{Cr}{\left(\text{OH}\right)}_3\left(aq\right)$

The above equation in balanced form is given as follows:

  $\stackrel{+6}{\text{Cr}}{\text{O}}_4^{2-}\left(aq\right)+4{\text{H}}_{\text{2}}\text{O}\left(l\right)+3e^{-}\to \stackrel{+3}{\text{Cr}}{\left(\text{OH}\right)}_3\left(aq\right)+5{\text{OH}}^{-}\left(aq\right)$

There is change in oxidation number of chromium.

The oxidation number of chromium is changed from $+6$ to $+3$ . So, chromium is reduced.

  ${\text{CrO}}_4^{2-}$ acts as an oxidizing agent in the reaction.

(d)

Interpretation Introduction

Interpretation: The half-reactions are to be balanced. The anions that act as an oxidizing or reducing agent is to be identified.

Concept Introduction: An equation illustrating just the reduction or just oxidation that occurs in a redox reaction is called a half-reaction. The oxidation and reduction half-reactions are written individually in the half-reaction approach before being compared to create a balanced redox equation.

Answer to Problem 80A

  ${\text{MnO}}_4^{-}$ acts as an oxidizing agent.

Explanation of Solution

An element is oxidized and acts as a reducing agent when its oxidation number rises.

The oxidizing agent is the element whose oxidation number decreases.

Consider the given half-reaction.

  ${\text{MnO}}_4^{-}\left(aq\right)\to {\text{Mn}}^{2+}\left(aq\right)$

The above equation in balanced form is given as follows:

  $\stackrel{+7}{\text{Mn}}{\text{O}}_4^{-}\left(aq\right)+8{\text{H}}^{+}+5e^{-}\to {\text{Mn}}^{2+}\left(aq\right)+4{\text{H}}_{\text{2}}\text{O}\left(l\right)$

There is change in oxidation number of manganese.

The oxidation number of manganese is changed from $+7$ to $+2$ . So, manganese is reduced.

  ${\text{MnO}}_4^{-}$ acts as an oxidizing agent in the reaction.

(e)

Interpretation Introduction

Interpretation: The half-reactions are to be balanced. The anions that act as an oxidizing or reducing agent is to be identified.

Concept Introduction: An equation illustrating just the reduction or just oxidation that occurs in a redox reaction is called a half-reaction. The oxidation and reduction half-reactions are written individually in the half-reaction approach before being compared to create a balanced redox equation.

Answer to Problem 80A

  ${\text{C}}_2{\text{O}}_4^{2-}$ acts as a reducing agent.

Explanation of Solution

An element is oxidized and acts as a reducing agent when its oxidation number rises.

The oxidizing agent is the element whose oxidation number decreases.

Consider the given half-reaction.

  ${\text{C}}_2{\text{O}}_4^{2-}\left(aq\right)\to {\text{CO}}_2\left(g\right)$

The above equation in balanced form is given as follows:

  $\stackrel{+3}{{\text{C}}_2}{\text{O}}_4^{2-}\left(aq\right)\to 2\stackrel{+4}{\text{C}}{\text{O}}_2\left(g\right)+2e^{-}$

There is change in oxidation number of carbon.

The oxidation number of chromium is changed from $+3$ to $+4$ . So, carbon is oxidized.

  ${\text{C}}_2{\text{O}}_4^{2-}$ acts as a reducing agent in the reaction.

(f)

Interpretation Introduction

Interpretation: The half-reactions are to be balanced. The anions that act as an oxidizing or reducing agent is to be identified.

Concept Introduction: An equation illustrating just the reduction or just oxidation that occurs in a redox reaction is called a half-reaction. The oxidation and reduction half-reactions are written individually in the half-reaction approach before being compared to create a balanced redox equation.

Answer to Problem 80A

  ${\text{MnO}}_4^{-}$ acts as an oxidizing agent.

Explanation of Solution

An element is oxidized and acts as a reducing agent when its oxidation number rises.

The oxidizing agent is the element whose oxidation number decreases.

Consider the given half-reaction.

  ${\text{MnO}}_4^{-}\left(aq\right)\to {\text{MnO}}_2\left(s\right)$

The above equation in balanced form is given as follows:

  $\stackrel{+7}{\text{Mn}}{\text{O}}_4^{-}\left(aq\right)+2{\text{H}}_2\text{O}\left(l\right)+3e^{-}\to \stackrel{+4}{\text{Mn}}{\text{O}}_2\left(s\right)+4{\text{OH}}^{-}\left(aq\right)$

There is change in oxidation number of manganese.

The oxidation number of chromium is changed from $+7$ to $+4$ . So, manganese is reduced.

  ${\text{MnO}}_4^{-}$ acts as an oxidizing agent in the reaction.