Chapter 18, Problem 115AE

The saturated calomel electrode. abbreviated SCE. is often used as a reference electrode in making electrochemica1 measurements. The SCE is composed of mercury in contact with a saturated solution of calomel (Hg₂Cl₂). The electrolyte solution is saturated KCI.  is +0.242 V relative to the standard hydrogen electrode. Calculate the potential for each of the following galvanic cells containing a saturated calomel electrode and the given half-cell components at standard conditions. In each case. indicate whether the SCE is the cathode or the anode. Standard reduction potentials are found in Table 17.1.

a. ${\text{Cu}}^{\text{2+}}+2{\text{e}}^{-}\to \text{Cu}$

b. ${\text{Fe}}^{3+}+{\text{e}}^{\text{-}}\to {\text{Fe}}^{2+}$

c. $\text{AgCl}\text{+}{\text{e}}^{\text{-}}\to \text{Ag}+{\text{Cl}}^{\text{-}}$

d. ${\text{Al}}^{3+}+3{\text{e}}^{-}\to \text{Al}$

e. ${\text{Ni}}^{2+}+2{\text{e}}^{-}\to \text{Ni}$

Interpretation Introduction

Interpretation:

The use of saturated Calomel electrode (SCE) as a reference electrode in making of electrochemical measurements and its formation by combination of Mercury and saturated solution of calomel $({\text{Hg}}_2{\text{Cl}}_2)$, which is present in contact with an electrolytic solution of saturated $\text{KCl}$ is given. The potential for the given galvanic cells containing calomel electrode and the given half-cell and the cathodic or anodic nature of SCE has to be calculated.

Concept introduction:

An electrode that is highly stable and whose electrode potential value is known is called reference electrode. The reference electrode is used for the construction of an electrochemical cell.

To determine: The potential for the given galvanic cell containing calomel electrode and the given half-cell components and the cathodic or anodic nature of SCE.

As the reduction potential of Copper is greater than the standard calomel electrode, therefore the standard calomel electrode acts as the anode, while the Copper electrode acts as the cathode.

The potential for the given galvanic cell containing calomel electrode and the given half-cell components is $\underset{\_}{0.098V}$.

Explanation of Solution

Given,

The value of $E_{\text{SCE}}$ is $+0.242\text{V}$.

The value of standard reduction potential for the given half-reaction is,

${\text{Cu}}^{2+}+2{\text{e}}^{-}\to \text{Cu}E°=0.34\text{V}$

As the reduction potential of Copper is greater than the standard calomel electrode, therefore the standard calomel electrode acts as the anode, while the Copper electrode acts as the cathode.

The reaction taking place at the cathode is,

${\text{Cu}}^{2+}+2{\text{e}}^{-}\to \text{Cu}E{°}_{\text{red}}=0.34\text{V}$

The reaction taking place at the anode is,

$2\text{Hg}+2{\text{Cl}}^{-}\to {\text{Hg}}_2{\text{Cl}}_2+2{\text{e}}^{-}E{°}_{\text{ox}}=-0.242\text{V}$

The value of $E{°}_{\text{cell}}$ is given as,

$E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}$

Where,

• $E{°}_{\text{ox}}$ is the oxidation potential of anode.

• $E{°}_{\text{red}}$ is the reduction potential of the cathode.

Substitute the values of $E{°}_{\text{ox}}$ and $E{°}_{\text{red}}$ in the above equation,

$\begin{array}{c}E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}\\ =\left(-0.242\text{V}\right)+0.34\text{V}\\ =\underset{\_}{0.098V}\end{array}$

The potential for the given galvanic cells containing calomel electrode and the given half-cell is $\underset{\_}{0.098V}$.

Interpretation Introduction

Interpretation:

The use of saturated Calomel electrode (SCE) as a reference electrode in making of electrochemical measurements and its formation by combination of Mercury and saturated solution of calomel $({\text{Hg}}_2{\text{Cl}}_2)$, which is present in contact with an electrolytic solution of saturated $\text{KCl}$ is given. The potential for the given galvanic cells containing calomel electrode and the given half-cell and the cathodic or anodic nature of SCE has to be calculated.

Concept introduction:

An electrode that is highly stable and whose electrode potential value is known is called reference electrode. The reference electrode is used for the construction of an electrochemical cell.

To determine: The potential for the given galvanic cells containing calomel electrode and the given half-cell components and the cathodic or anodic nature of SCE.

As the reduction potential of Iron is greater than the standard calomel electrode, therefore the standard calomel electrode acts as the anode, while the Iron electrode acts as the cathode.

The potential for the given galvanic cell containing calomel electrode and the given half-cell components is $\underset{\_}{0.528V}$.

Explanation of Solution

Explanation

Given

The value of $E_{\text{SCE}}$ is $+0.242\text{V}$.

The value of standard reduction potential for the given half-reaction is,

${\text{Fe}}^{3+}+3{\text{e}}^{-}\to \text{Fe}E°=0.77\text{V}$

As the reduction potential of Iron is greater than the standard calomel electrode, therefore the standard calomel electrode acts as the anode, while the Iron electrode acts as the cathode.

The reaction taking place at the cathode is,

${\text{Fe}}^{3+}+3{\text{e}}^{-}\to \text{Fe}E{°}_{\text{red}}=0.77\text{V}$

The reaction taking place at the anode is,

$2\text{Hg}+2{\text{Cl}}^{-}\to {\text{Hg}}_2{\text{Cl}}_2+2{\text{e}}^{-}E{°}_{\text{ox}}=-0.242\text{V}$

The value of $E{°}_{\text{cell}}$ is given as,

$E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}$

Where,

• $E{°}_{\text{ox}}$ is the oxidation potential of anode.

• $E{°}_{\text{red}}$ is the reduction potential of the cathode.

Substitute the values of $E{°}_{\text{ox}}$ and $E{°}_{\text{red}}$ in the above equation,

$\begin{array}{c}E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}\\ =\left(-0.242\text{V}\right)+0.77\text{V}\\ =\underset{\_}{0.528V}\end{array}$

The potential for the given galvanic cells containing calomel electrode and the given half-cell components is $\underset{\_}{0.528V}$.

Interpretation Introduction

Interpretation:

The use of saturated Calomel electrode (SCE) as a reference electrode in making of electrochemical measurements and its formation by combination of Mercury and saturated solution of calomel $({\text{Hg}}_2{\text{Cl}}_2)$, which is present in contact with an electrolytic solution of saturated $\text{KCl}$ is given. The potential for the given galvanic cells containing calomel electrode and the given half-cell and the cathodic or anodic nature of SCE has to be calculated.

Concept introduction:

An electrode that is highly stable and whose electrode potential value is known is called reference electrode. The reference electrode is used for the construction of an electrochemical cell.

To determine: The potential for the given galvanic cell containing calomel electrode and the given half-cell and the cathodic or anodic nature of SCE.

As the reduction potential of $\text{AgCl}$ is lower than the standard calomel electrode, therefore the standard calomel electrode acts as the cathode, while the $\text{AgCl}$ electrode acts as the anode.

The potential for the given galvanic cell containing calomel electrode and the given half-cell components is $\underset{\_}{0.022V}$.

Explanation of Solution

Explanation

Given

The value of $E_{\text{SCE}}$ is $+0.242\text{V}$.

The value of standard reduction potential for the given half-reaction is,

$\text{AgCl}+{\text{e}}^{-}\to \text{Ag}+{\text{Cl}}^{-}E°=0.22\text{V}$

As the reduction potential of $\text{AgCl}$ is lower than the standard calomel electrode, therefore the standard calomel electrode acts as the cathode, while the $\text{AgCl}$ electrode acts as the anode.

The reaction taking place at the cathode is,

${\text{Hg}}_2{\text{Cl}}_2+2{\text{e}}^{-}\to 2\text{Hg}+2{\text{Cl}}^{-}E{°}_{\text{red}}=0.242\text{V}$

The reaction taking place at the anode is,

$\text{Ag}+{\text{Cl}}^{-}\to \text{AgCl}+{\text{e}}^{-}E{°}_{\text{ox}}=0.22\text{V}$

The value of $E{°}_{\text{cell}}$ is given as,

$E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}$

Where,

• $E{°}_{\text{ox}}$ is the oxidation potential of the anode.

• $E{°}_{\text{red}}$ is the reduction potential of the cathode.

Substitute the values of $E{°}_{\text{ox}}$ and $E{°}_{\text{red}}$ in the above equation,

$\begin{array}{c}E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}\\ =\left(-0.22\text{V}\right)+0.242\text{V}\\ =\underset{\_}{0.022V}\end{array}$

The potential for the given galvanic cells containing calomel electrode and the given half-cell is $\underset{\_}{0.022V}$.

Interpretation Introduction

Interpretation:

The use of saturated Calomel electrode (SCE) as a reference electrode in making of electrochemical measurements and its formation by combination of Mercury and saturated solution of calomel $({\text{Hg}}_2{\text{Cl}}_2)$, which is present in contact with an electrolytic solution of saturated $\text{KCl}$ is given. The potential for the given galvanic cells containing calomel electrode and the given half-cell and the cathodic or anodic nature of SCE has to be calculated.

Concept introduction:

An electrode that is highly stable and whose electrode potential value is known is called reference electrode. The reference electrode is used for the construction of an electrochemical cell.

To determine: The potential for the given galvanic cell containing calomel electrode and the given half-cell components and the cathodic or anodic nature of SCE.

As the reduction potential of Aluminum is lower than the standard calomel electrode, therefore the standard calomel electrode acts as the cathode, while the Aluminum electrode acts as the anode.

The potential for the given galvanic cell containing calomel electrode and the given half-cell components is $\underset{\_}{1.902V}$.

Explanation of Solution

Given,

The value of $E_{\text{SCE}}$ is $+0.242\text{V}$.

The value of standard reduction potential for the given half-reaction is,

${\text{Al}}^{\text{3+}}+3{\text{e}}^{-}\to \text{Al}E°=-1.66\text{V}$

As the reduction potential of Aluminum is lower than the standard calomel electrode, therefore the standard calomel electrode acts as the cathode, while the Aluminum electrode acts as the anode.

The reaction taking place at the cathode is,

${\text{Hg}}_2{\text{Cl}}_2+2{\text{e}}^{-}\to 2\text{Hg}+2{\text{Cl}}^{-}E{°}_{\text{red}}=0.242\text{V}$

The reaction taking place at the anode is,

$\text{Al}\to {\text{Al}}^{\text{3+}}+3{\text{e}}^{-}E{°}_{\text{ox}}=1.66\text{V}$

The value of $E{°}_{\text{cell}}$ is given as,

$E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}$

Where,

• $E{°}_{\text{ox}}$ is the oxidation potential of the anode.

• $E{°}_{\text{red}}$ is the reduction potential of the cathode.

Substitute the values of $E{°}_{\text{ox}}$ and $E{°}_{\text{red}}$ in the above equation,

$\begin{array}{c}E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}\\ =\left(1.66\text{V}\right)+0.242\text{V}\\ =\underset{\_}{1.902V}\end{array}$

The potential for the given galvanic cell containing calomel electrode and the given half-cell components is $\underset{\_}{1.902V}$.

Interpretation Introduction

Interpretation:

The use of saturated Calomel electrode (SCE) as a reference electrode in making of electrochemical measurements and its formation by combination of Mercury and saturated solution of calomel $({\text{Hg}}_2{\text{Cl}}_2)$, which is present in contact with an electrolytic solution of saturated $\text{KCl}$ is given. The potential for the given galvanic cells containing calomel electrode and the given half-cell and the cathodic or anodic nature of SCE has to be calculated.

Concept introduction:

An electrode that is highly stable and whose electrode potential value is known is called reference electrode. The reference electrode is used for the construction of an electrochemical cell.

To determine: The potential for the given galvanic cell containing calomel electrode and the given half-cell components and the cathodic or anodic nature of SCE.

As the reduction potential of Nickel is lower than the standard calomel electrode, therefore the standard calomel electrode acts as the cathode, while the Nickel electrode acts as the anode.

The potential for the given galvanic cell containing calomel electrode and the given half-cell components is $\underset{\_}{0.472V}$.

Explanation of Solution

Given,

The value of $E_{\text{SCE}}$ is $+0.242\text{V}$.

The value of standard reduction potential for the given half-reaction is,

${\text{Ni}}^{\text{2+}}+2{\text{e}}^{-}\to \text{Ni}E°=-0.23\text{V}$

As the reduction potential of Nickel is lower than the standard calomel electrode, therefore the standard calomel electrode acts as the cathode, while the Nickel electrode acts as the anode.

The reaction taking place at the cathode is,

${\text{Hg}}_2{\text{Cl}}_2+2{\text{e}}^{-}\to 2\text{Hg}+2{\text{Cl}}^{-}E{°}_{\text{red}}=0.242\text{V}$

The reaction taking place at the anode is,

$\text{Ni}\to {\text{Ni}}^{\text{2+}}+2{\text{e}}^{-}E{°}_{\text{ox}}=0.23\text{V}$

The value of $E{°}_{\text{cell}}$ is given as,

$E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}$

Where,

• $E{°}_{\text{ox}}$ is the oxidation potential of the anode.

• $E{°}_{\text{red}}$ is the reduction potential of the cathode.

Substitute the values of $E{°}_{\text{ox}}$ and $E{°}_{\text{red}}$ in the above equation,

$\begin{array}{c}E°cell=E{°}_{\text{ox}}+E{°}_{\text{red}}\\ =0.23\text{V}+0.242\text{V}\\ =\underset{\_}{0.472V}\end{array}$

The potential for the given galvanic cells containing calomel electrode and the given half-cell is $\underset{\_}{0.472V}$.