Chapter 21, Problem 21.11P

(a)

Interpretation Introduction

Interpretation:

The species that is being oxidized in the given balanced redox reaction has to be identified.

$2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)$

Concept Introduction:

An electrochemical cell is a device in which a redox reaction is used to convert chemical energy into electrical energy. Such device is also known as the galvanic or voltaic cell.

Galvanic cell consists of two half-cells. The redox reaction occurs in these half-cells. The half-cell in which the reduction reaction occurs is known as the reduction half-cell, whereas the half-cell in which the oxidation reaction occurs is known as the oxidation half-cell.

Anode: The electrode where the oxidation occurs is called as an anode. It is a negatively charged electrode.

Cathode: The electrode where reduction occurs is called as a cathode. It is a positively charged electrode.

Oxidation: The gain of oxygen or the loss of hydrogen or the loss of an electron in a species during a redox reaction is called as oxidation.

Reduction: The loss of oxygen or the gain of hydrogen or the gain of an electron in a species during a redox reaction is called as reduction.

Explanation of Solution

From given redox reaction the species that is being oxidized is identified by using the oxidation number of the species. The species that gets oxidized will results to have increased oxidation number.

First, the oxidation number for each species in redox reaction is determined as follows,

$\begin{array}{l}3\text{-1}\text{+1}\text{-2}\text{+1}\text{-2}\text{ +6}\text{-2 0 }\text{-2}\text{+1}\\ 2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)\end{array}$

Therefore, it is clear that ${\text{CrO}}_{\text{2}}{}^{\text{-}}$ is oxidized since its oxidation number increases from +3 in reactant side to +6 in product side.

(b)

Interpretation Introduction

Interpretation:

The species that is being reduced in the given redox reaction has to be identified.

$2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)$

Concept Introduction:

An electrochemical cell is a device in which a redox reaction is used to convert chemical energy into electrical energy. Such device is also known as the galvanic or voltaic cell.

Galvanic cell consists of two half-cells. The redox reaction occurs in these half-cells. The half-cell in which the reduction reaction occurs is known as the reduction half-cell, whereas the half-cell in which the oxidation reaction occurs is known as the oxidation half-cell.

Anode: The electrode where the oxidation occurs is called as an anode. It is a negatively charged electrode.

Cathode: The electrode where reduction occurs is called as a cathode. It is a positively charged electrode.

Oxidation: The gain of oxygen or the loss of hydrogen or the loss of an electron in a species during a redox reaction is called as oxidation.

Reduction: The loss of oxygen or the gain of hydrogen or the gain of an electron in a species during a redox reaction is called as reduction.

Explanation of Solution

From given redox reaction the species that is being reduced is identified by using the oxidation number of the species. The species that gets reduced will results to have decreased oxidation number.

First, the oxidation number for each species in redox reaction is determined as follows,

$\begin{array}{l}3\text{-1}\text{+1}\text{-2}\text{+1}\text{-2}\text{ +6}\text{-2 0 }\text{-2}\text{+1}\\ 2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)\end{array}$

Therefore, it is clear that $Cl{O}^{\text{-}}$ is reduced since its oxidation number decreases from +1 in reactant side to 0 in product side.

(c)

Interpretation Introduction

Interpretation:

The oxidizing agent in the given redox reaction has to be identified.

$2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)$

Concept Introduction:

An electrochemical cell is a device in which a redox reaction is used to convert chemical energy into electrical energy. Such device is also known as the galvanic or voltaic cell.

Galvanic cell consists of two half-cells. The redox reaction occurs in these half-cells. The half-cell in which the reduction reaction occurs is known as the reduction half-cell, whereas the half-cell in which the oxidation reaction occurs is known as the oxidation half-cell.

Anode: The electrode where the oxidation occurs is called as an anode. It is a negatively charged electrode.

Cathode: The electrode where reduction occurs is called as a cathode. It is a positively charged electrode.

Oxidation: The gain of oxygen or the loss of hydrogen or the loss of an electron in a species during a redox reaction is called as oxidation.

Reduction: The loss of oxygen or the gain of hydrogen or the gain of an electron in a species during a redox reaction is called as reduction.

Reducing agent: The substance that reduces other species and gets oxidized is called as a reducing agent.

Oxidizing agent: The substance that oxidizes other species and gets reduced is called as an oxidizing agent.

Explanation of Solution

The substance that is reduced is called as an oxidizing agent. From given redox reaction the species that is being reduced is identified by using the oxidation number of the species. The species that gets reduced will results to have decreased oxidation number.

First, the oxidation number for each species in redox reaction is determined as follows,

$\begin{array}{l}3\text{-1}\text{+1}\text{-2}\text{+1}\text{-2}\text{ +6}\text{-2 0 }\text{-2}\text{+1}\\ 2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)\end{array}$

Therefore, it is clear that $Cl{O}^{\text{-}}$ is reduced since its oxidation number decreases from +1 in reactant side to 0 in product side.

Hence, the oxidizing agent is $Cl{O}^{\text{-}}$.

(d)

Interpretation Introduction

Interpretation:

The reducing agent in the given redox reaction has to be identified.

$2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)$

Concept Introduction:

An electrochemical cell is a device in which a redox reaction is used to convert chemical energy into electrical energy. Such device is also known as the galvanic or voltaic cell.

Galvanic cell consists of two half-cells. The redox reaction occurs in these half-cells. The half-cell in which the reduction reaction occurs is known as the reduction half-cell, whereas the half-cell in which the oxidation reaction occurs is known as the oxidation half-cell.

Anode: The electrode where the oxidation occurs is called as an anode. It is a negatively charged electrode.

Cathode: The electrode where reduction occurs is called as a cathode. It is a positively charged electrode.

Oxidation: The gain of oxygen or the loss of hydrogen or the loss of an electron in a species during a redox reaction is called as oxidation.

Reduction: The loss of oxygen or the gain of hydrogen or the gain of an electron in a species during a redox reaction is called as reduction.

Reducing agent: The substance that reduces other species and gets oxidized is called as a reducing agent.

Oxidizing agent: The substance that oxidizes other species and gets reduced is called as an oxidizing agent.

Explanation of Solution

The substance that reduces other species and gets oxidized is called as a reducing agent.

From given redox reaction the species that is being oxidized is identified by using the oxidation number of the species. The species that gets oxidized will results to have increased oxidation number.

First, the oxidation number for each species in redox reaction is determined as follows,

$\begin{array}{l}3\text{-1}\text{+1}\text{-2}\text{+1}\text{-2}\text{ +6}\text{-2 0 }\text{-2}\text{+1}\\ 2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)\end{array}$

Therefore, it is clear that ${\text{CrO}}_{\text{2}}{}^{\text{-}}$ is oxidized since its oxidation number increases from +3 in reactant side to +6 in product side. Therefore the reducing agent is ${\text{CrO}}_{\text{2}}{}^{\text{-}}$.

(e)

Interpretation Introduction

Interpretation:

Between which species the electron transfers occur has to be determined.

$2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)$

Concept Introduction:

An electrochemical cell is a device in which a redox reaction is used to convert chemical energy into electrical energy. Such device is also known as the galvanic or voltaic cell.

Galvanic cell consists of two half-cells. The redox reaction occurs in these half-cells. The half-cell in which the reduction reaction occurs is known as the reduction half-cell, whereas the half-cell in which the oxidation reaction occurs is known as the oxidation half-cell.

The electrons flow from anode to cathode through the external wire of the circuit. A salt bridge is used to complete the cell circuit.

Salt bridge: It is a U-shaped tube filled with concentrated solution of inert electrolytes such as $\text{KCl,}{\text{KNO}}_{\text{3}}\text{and so on}\text{.}$. The ions that are present in the tube do not take part in the reaction.

Anode: The electrode where the oxidation occurs is called as an anode. It is a negatively charged electrode.

Cathode: The electrode where reduction occurs is called as a cathode. It is a positively charged electrode.

Explanation of Solution

From given redox reaction the species that is being oxidized is identified by using the oxidation number of the species. The species that gets oxidized will results to have increased oxidation number.

First, the oxidation number for each species in redox reaction is determined as follows,

$\begin{array}{l}3\text{-1}\text{+1}\text{-2}\text{+1}\text{-2}\text{ +6}\text{-2 0 }\text{-2}\text{+1}\\ 2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)\end{array}$

Therefore, it is clear that ${\text{CrO}}_{\text{2}}{}^{\text{-}}$ is oxidized since its oxidation number increases from +3 in reactant side to +6 in product side.

It is clear that $Cl{O}^{\text{-}}$ is reduced since its oxidation number decreases from +1 in reactant side to 0 in product side.

Hence, the electron flow from ${\text{CrO}}_{\text{2}}{}^{\text{-}}$ to $Cl{O}^{\text{-}}$.

(f)

Interpretation Introduction

Interpretation:

The balanced molecular equation with given spectator ion ${\text{Na}}^{\text{+}}$ has to be determined.

$2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)$

Concept Introduction:

An electrochemical cell is a device in which a redox reaction is used to convert chemical energy into electrical energy. Such device is also known as the galvanic or voltaic cell.

Galvanic cell consists of two half-cells. The redox reaction occurs in these half-cells. The half-cell in which the reduction reaction occurs is known as the reduction half-cell, whereas the half-cell in which the oxidation reaction occurs is known as the oxidation half-cell.

The electrons flow from anode to cathode through the external wire of the circuit. A salt bridge is used to complete the cell circuit.

Salt bridge: It is a U-shaped tube filled with concentrated solution of inert electrolytes such as $\text{KCl,}{\text{KNO}}_{\text{3}}\text{and so on}\text{.}$. The ions that are present in the tube do not take part in the reaction.

Anode: The electrode where the oxidation occurs is called as an anode. It is a negatively charged electrode.

Cathode: The electrode where reduction occurs is called as a cathode. It is a positively charged electrode.

Explanation of Solution

The given redox reaction is as follows,

$2Cr{O}_2^{-}\left(aq\right)+2H_{2}O\left(l\right)+6Cl{O}^{-}\left(aq\right)\to 2Cr{O}_4^{2-}\left(aq\right)+3C{l}_2\left(g\right)+4O{H}^{-}\left(aq\right)$

Using the given spectator ion the balanced molecular equation is as follows,

$2NaCr{O}_2^{}\left(aq\right)+2H_{2}O\left(l\right)+6NaCl{O}^{}\left(aq\right)\to 2N{a}_{2}Cr{O}_4^{}\left(aq\right)+3C{l}_2\left(g\right)+4NaO{H}^{}\left(aq\right)$