Chapter 17, Problem 12PE

(a)

Interpretation Introduction

Interpretation:

Whether below unbalanced reaction is balanced correctly or not has to be determined. Also, unbalanced equation has to be balanced.

  ${\text{MnO}}_{\text{2}}\left(s\right)+\text{Al}\left(s\right)\to \text{Mn}\left(s\right)+{\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}\left(s\right)$

Concept Introduction:

Oxidation process represents loss of electrons. Reduction process represents gain of electrons. Oxidation numbers are the part of system that is formed to track electrons in reaction. Balanced chemical reactions are those that have equal number of atoms on both sides of arrow.

(b)

Interpretation Introduction

Interpretation:

Whether below unbalanced reaction is balanced correctly or not has to be determined. Also, unbalanced equation has to be balanced.

  $\text{Cu}\left(s\right)+{\text{Ag}}^{+}\left(aq\right)\to {\text{Cu}}^{+2}\left(aq\right)+\text{Ag}\left(s\right)$

Concept Introduction:

Refer to part (a).

(c)

Interpretation Introduction

Interpretation:

Whether below unbalanced reaction is balanced correctly or not has to be determined. Also, unbalanced equation has to be balanced.

  $\text{Br}\left(aq\right)+{\text{MnO}}_{\text{4}}\left(aq\right)\to {\text{Br}}_2\left(l\right)+{\text{Mn}}^{+2}\left(aq\right)$

Concept Introduction:

Rules to balance redox reactions by ion-electron method are as follows:

1. Two half-reactions with elements that got oxidized and reduced should be written.

2. Elements other than oxygen and hydrogen should be balanced.

3. Conditions to balance $\text{O}$ and $\text{H}$ are as follows:

In acidic solution, ${\text{H}}^{+}$ and ${\text{H}}_2\text{O}$ should be used to balance $\text{O}$ and $\text{H}$.

In basic solution, equal ${\text{OH}}^{-}$ ions to ${\text{H}}^{+}$ ions should be added on both sides of balanced reaction in acidic medium.

4. For acidic medium, charge is balanced by addition of ${\text{H}}^{+}$ ion. Then combine ${\text{H}}^{+}$ and ${\text{OH}}^{-}$ to form ${\text{H}}_2\text{O}$ and cancel common ${\text{H}}_2\text{O}$ in reaction.

5. Electrons should be added to balance electric charge.

6. Finally, two half-reactions should be added and any common substance including electrons must be cancelled.

(d)

Interpretation Introduction

Interpretation:

Whether below unbalanced reaction is balanced correctly or not has to be determined. Also, unbalanced equation has to be balanced.

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

Concept Introduction:

Refer to part (c).