Chapter 19, Problem 54E

Interpretation Introduction

(a)

Interpretation:

The statement that oxidation and reduction occur at electrodes in a voltaic cell is to be classified as true or false.

Concept introduction:

The process in which oxygen is added or a hydrogen atom is removed from a substance is known as oxidation and the process in which hydrogen is added or an oxygen atom is removed from a substance is known as reduction. The addition of an electronegative atom to another substance is also known as oxidation and the addition of an electropositive atom to another substance is known as reduction. A reducing agent is a substance that undergoes oxidation and an oxidizing agent is a substance that undergoes reduction.

Answer to Problem 54E

The statement that oxidation and reduction occur at electrodes in a voltaic cell is true.

Explanation of Solution

A voltaic cell is the cell in which the chemical energy, which is produced by a redox reaction, is changed to electrical energy. In a voltaic cell, both oxidation and reduction reactions take place. At the anode, oxidation takes place and at the cathode, reduction takes place. Therefore, oxidation and reduction occur at electrodes in a voltaic cell.

Conclusion

The statement that oxidation and reduction occur at electrodes in a voltaic cell is true.

Interpretation Introduction

(b)

Interpretation:

The statement that the sum of the oxidation numbers is zero in a molecular compound, but that sum may or may not be zero in an ionic compound is to be classified as true or false.

Concept introduction:

The process in which oxygen is added or a hydrogen atom is removed from a substance is known as oxidation and the process in which hydrogen is added or an oxygen atom is removed from a substance is known as reduction. The addition of an electronegative atom to another substance is also known as oxidation and the addition of an electropositive atom to another substance is known as reduction. A reducing agent is a substance that undergoes oxidation and an oxidizing agent is a substance that undergoes reduction.

Answer to Problem 54E

The statement that the sum of the oxidation numbers is zero in a molecular compound, but that sum may or may not be zero in an ionic compound is false.

Explanation of Solution

The sum of the oxidation numbers in a molecular compound is equal to zero. For example, ${\text{H}}_{\text{2}}\text{O}$ and ${\text{CO}}_{\text{2}}$. The sum of the oxidation numbers, in the case of an ionic compound, is equal to the charge present on the ionic species. Therefore, the statement that the sum of the oxidation numbers is zero in a molecular compound, but that sum may or may not be zero in an ionic compound is false.

Conclusion

The statement that the sum of the oxidation numbers is zero in a molecular compound, but that sum may or may not be zero in an ionic compound is false.

Interpretation Introduction

(c)

Interpretation:

The statement that the oxidation number of oxygen is the same in the compounds ${\text{O}}^{2-}$, ${\text{HClO}}_{\text{3}}$, ${\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{2-}$ and ${\text{NO}}_{\text{2}}$ is to be classified as true or false.

Concept introduction:

The process in which oxygen is added or a hydrogen atom is removed from a substance is known as oxidation and the process in which hydrogen is added or an oxygen atom is removed from a substance is known as reduction. The addition of an electronegative atom to another substance is also known as oxidation and the addition of an electropositive atom to another substance is known as reduction. A reducing agent is a substance that undergoes oxidation and an oxidizing agent is a substance that undergoes reduction.

Answer to Problem 54E

The statement that the oxidation number of oxygen is the same in the compounds ${\text{O}}^{2-}$, ${\text{HClO}}_{\text{3}}$, ${\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{2-}$ and ${\text{NO}}_{\text{2}}$ is true.

Explanation of Solution

The oxidation number of ${\text{O}}^{2-}$ is $-2$.

The oxidation number of $\text{O}$ in ${\text{HClO}}_{\text{3}}$ is calculated as shown below.

$\text{Charge}\text{on}{\text{HClO}}_{\text{3}}=\text{O}\text{.N}\text{of}\text{H}+\text{O}\text{.N}\text{of}\text{Cl}+\text{3}\left(\text{O}\text{.N}\text{of}\text{O}\right)$

Substitute the values of charge on ${\text{HClO}}_{\text{3}}$, oxidation numbers of $\text{H}$ and $\text{Cl}$ in the above expression.

$\begin{array}{rll}\text{Charge}\text{on}{\text{HClO}}_{\text{3}}& =& \text{O}\text{.N}\text{of}\text{H}+\text{O}\text{.N}\text{of}\text{Cl}+\text{3}\left(\text{O}\text{.N}\text{of}\text{O}\right)\\ 0& =& +1+\left(+5\right)+3x\\ x& =& -2\end{array}$

Therefore, the oxidation number of $\text{O}$ in ${\text{HClO}}_{\text{3}}$ is $-2$.

The oxidation number of $\text{O}$ in ${\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{2-}$ is calculated as shown below.

$\text{Charge}\text{on}{\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{2-}=2\left(\text{O}\text{.N}\text{of}\text{S}\right)+3\left(\text{O}\text{.N}\text{of}\text{O}\right)$

Substitute the values of charge on ${\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{2-}$ and oxidation number of $\text{S}$ in the above expression.

$\begin{array}{rll}\text{Charge}\text{on}{\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{2-}& =& 2\left(\text{O}\text{.N}\text{of}\text{S}\right)+3\left(\text{O}\text{.N}\text{of}\text{O}\right)\\ -2& =& 2\left(+2\right)+3x\\ x& =& -2\end{array}$

Therefore, the oxidation number of $\text{O}$ in ${\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{2-}$ is $-2$.

The oxidation number of $\text{O}$ in ${\text{NO}}_{\text{2}}$ is calculated as shown below.

$\text{Charge}\text{on}{\text{NO}}_{\text{2}}=\text{O}\text{.N}\text{of}\text{N}+2\left(\text{O}\text{.N}\text{of}\text{O}\right)$

Substitute the values of charge on ${\text{NO}}_{\text{2}}$ and oxidation number of $\text{N}$ in the above expression.

$\begin{array}{rll}\text{Charge}\text{on}{\text{NO}}_{\text{2}}& =& \text{O}\text{.N}\text{of}\text{N}+2\left(\text{O}\text{.N}\text{of}\text{O}\right)\\ 0& =& +4+2x\\ x& =& -2\end{array}$

Therefore, the oxidation number of $\text{O}$ in ${\text{NO}}_{\text{2}}$ is $-2$.

The oxidation number of oxygen is the same in the compounds ${\text{O}}^{2-}$, ${\text{HClO}}_{\text{3}}$, ${\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{2-}$ and ${\text{NO}}_{\text{2}}$.

Conclusion

The statement that the oxidation number of oxygen is the same in the compounds ${\text{O}}^{2-}$, ${\text{HClO}}_{\text{3}}$, ${\text{S}}_{\text{2}}{\text{O}}_{\text{3}}{}^{2-}$ and ${\text{NO}}_{\text{2}}$ is true.

Interpretation Introduction

(d)

Interpretation:

The statement that the oxidation number of alkali metals is always $-1$ is to be classified as true or false.

Concept introduction:

The process in which oxygen is added or a hydrogen atom is removed from a substance is known as oxidation and the process in which hydrogen is added or an oxygen atom is removed from a substance is known as reduction. The addition of an electronegative atom to another substance is also known as oxidation and the addition of an electropositive atom to another substance is known as reduction. A reducing agent is a substance that undergoes oxidation and an oxidizing agent is a substance that undergoes reduction.

Answer to Problem 54E

The statement that the oxidation number of alkali metals is always $-1$ is false.

Explanation of Solution

The alkali metals are the elements present in the group $1$ of the periodic table. They possess only one electron in their outermost valence shell. The alkali metals lose one electron from their outermost shell to attain the configuration of a noble gas. Therefore, they have an oxidation number of $+1$.

Conclusion

The statement that the oxidation number of alkali metals is always $-1$ is false.

Interpretation Introduction

(e)

Interpretation:

The statement that a substance that gains electrons is oxidized is to be classified as true or false.

Concept introduction:

The process in which oxygen is added or a hydrogen atom is removed from a substance is known as oxidation and the process in which hydrogen is added or an oxygen atom is removed from a substance is known as reduction. The addition of an electronegative atom to another substance is also known as oxidation and the addition of an electropositive atom to another substance is known as reduction. A reducing agent is a substance that undergoes oxidation and an oxidizing agent is a substance that undergoes reduction.

Answer to Problem 54E

The statement that a substance that gains electrons is oxidized is false.

Explanation of Solution

Reduction is the process in which a substance gains electrons, whereas oxidation is the process in which a substance loses electrons. Therefore, a substance that gains electrons is said to be reduced.

Conclusion

The statement that a substance that gains electrons is oxidized is false.

Interpretation Introduction

(f)

Interpretation:

The statement that a strong reducing agent has a strong attraction for electrons is to be classified as true or false.

Concept introduction:

The process in which oxygen is added or a hydrogen atom is removed from a substance is known as oxidation and the process in which hydrogen is added or an oxygen atom is removed from a substance is known as reduction. The addition of an electronegative atom to another substance is also known as oxidation and the addition of an electropositive atom to another substance is known as reduction. A reducing agent is a substance that undergoes oxidation and an oxidizing agent is a substance that undergoes reduction.

Answer to Problem 54E

The statement that a strong reducing agent has a strong attraction for electrons is false.

Explanation of Solution

A reducing agent is a substance that undergoes oxidation in a redox reaction. During oxidation, the substance has a tendency to lose electrons. This means that a strong reducing agent does not have a strong attraction for electrons.

Conclusion

The statement that a strong reducing agent has a strong attraction for electrons is false.

Interpretation Introduction

(g)

Interpretation:

The statement that the favored side of a redox equilibrium equation is the side with the weaker oxidizer and reducer is to be classified as true or false.

Concept introduction:

The process in which oxygen is added or a hydrogen atom is removed from a substance is known as oxidation and the process in which hydrogen is added or an oxygen atom is removed from a substance is known as reduction. The addition of an electronegative atom to another substance is also known as oxidation and the addition of an electropositive atom to another substance is known as reduction. A reducing agent is a substance that undergoes oxidation and an oxidizing agent is a substance that undergoes reduction.

Answer to Problem 54E

The statement that the favored side of a redox equilibrium equation is the side with the weaker oxidizer and reducer is true.

Explanation of Solution

In a redox reaction, the reducing agent is known as the reducer and the oxidizing agent is known as the oxidizer. The reducer loses electrons and these electrons are gained by the oxidizer. The stronger reducer and the stronger oxidizer react to form the weaker reducer and the weaker oxidizer. At equilibrium, the weaker reducer and the weaker oxidizer are favored.

Conclusion

The statement that the favored side of a redox equilibrium equation is the side with the weaker oxidizer and reducer is true.