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CBSE - Class 12 Chemistry Electrochemistry Worksheet
The conductivity of sodium chloride at 298 K has been determined at different concentrations and the results are given below:

Calculate (\Lambda_{m}) for all concentrations and draw a plot between (\Lambda_{m}) and (c^{1/2}). Find the value of (\Lambda^{0}_{m}).
Worksheet Answers
Solution:
The molar conductivity ($\Lambda_m$) is defined by the relationship between conductivity ($\kappa$) and the concentration of the electrolyte ($C$). The formula is given by:
$\Lambda_m = \frac{\kappa \times 1000}{C}$
Given Variables:
Calculation:
$\Lambda_m = \frac{7.896 \times 10^{-5} \, \text{S cm}^{-1} \times 1000 \, \text{cm}^3 \text{L}^{-1}}{0.00241 \, \text{mol L}^{-1}}$
$\Lambda_m = \frac{0.07896}{0.00241} \, \text{S cm}^2 \text{mol}^{-1}$
$\Lambda_m \approx 32.76 \, \text{S cm}^2 \text{mol}^{-1}$ [Per the definition of Molar Conductivity]
The degree of dissociation ($\alpha$) relates the molar conductivity at a given concentration to the molar conductivity at infinite dilution ($\Lambda^0_m$).
$\alpha = \frac{\Lambda_m}{\Lambda^0_m}$
Given Variables:
Calculation:
$\alpha = \frac{32.76}{390.5} \approx 0.0839$ [By the Arrhenius theory of electrolytic dissociation]
For a weak electrolyte like acetic acid ($CH_3COOH \rightleftharpoons CH_3COO^- + H^+$), the dissociation constant is determined using Ostwald’s Dilution Law:
$K_a = \frac{C \alpha^2}{1 - \alpha}$
Variables:
Calculation:
$K_a = \frac{0.00241 \times (0.0839)^2}{1 - 0.0839}$
$K_a = \frac{0.00241 \times 0.007039}{0.9161}$
$K_a = \frac{0.00001696}{0.9161} \approx 1.85 \times 10^{-5}$
Final Solution: The molar conductivity of acetic acid is $32.76 \, \text{S cm}^2 \text{mol}^{-1}$ and its dissociation constant $K_a$ is $1.85 \times 10^{-5}$.
Solution:
To determine the amount of electricity required, we must first determine the change in the oxidation state of Iron ($Fe$) during the transformation of $FeO$ to $Fe_{2}O_{3}$.
The transformation involves the oxidation of $Fe^{2+}$ to $Fe^{3+}$. For 1 mole of $FeO$, the chemical equation is:
$FeO \rightarrow \frac{1}{2} Fe_{2}O_{3} + e^{-}$
Alternatively, looking at the oxidation of the iron atom: $Fe^{2+} \rightarrow Fe^{3+} + 1e^{-}$.
Since we are oxidizing 1 mole of $FeO$, which contains 1 mole of $Fe^{2+}$ ions, 1 mole of electrons is involved in the transfer. [By Law of Conservation of Charge].
The total charge ($Q$) required is given by the product of the number of moles of electrons ($n$) and Faraday's constant ($F$).
Applying the Faraday's Law of Electrolysis relationship:
$Q = n \times F$
$Q = 1 \text{ mol} \times 96500 \text{ C mol}^{-1}$
$Q = 96500 \text{ C}$
Final Solution: The electricity required for the oxidation of 1 mol of FeO to Fe_{2}O_{3} is 96500 C.
Solution:
To determine the standard Gibbs energy change ($\Delta_{r}G^{o}$) and standard cell potential ($E^{o}_{cell}$), we must first analyze the redox components of the cell reaction:
[Per Standard Electrode Potential Tables (IUPAC convention)]
The standard cell potential is the algebraic sum of the standard reduction potentials of the cathode and the anode:
$E^{o}_{cell} = E^{o}_{cathode} - E^{o}_{anode}$
$E^{o}_{cell} = 0.344\,V - (-0.76\,V)$
$E^{o}_{cell} = 0.344\,V + 0.76\,V = 1.104\,V$
The relationship between the standard Gibbs energy and standard cell potential is governed by the Nernstian thermodynamic equation:
$\Delta_{r}G^{o} = -nFE^{o}_{cell}$
Where:
Substituting the values:
$\Delta_{r}G^{o} = -(2\,mol\,e^{-}) \times (96487\,C\,mol^{-1}) \times (1.104\,J\,C^{-1})$
$\Delta_{r}G^{o} = -213043.584\,J\,mol^{-1}$
$\Delta_{r}G^{o} \approx -213.04\,kJ\,mol^{-1}$
| Parameter | Calculated Value |
|---|---|
| Standard Cell Potential ($E^{o}$) | $1.104\,V$ |
| Standard Gibbs Energy ($\Delta_{r}G^{o}$) | $-213.04\,kJ\,mol^{-1}$ |
Final Solution: The standard cell potential $E^{o}$ is $1.104\,V$ and the standard Gibbs energy change $\Delta_{r}G^{o}$ is $-213.04\,kJ\,mol^{-1}$.
Solution:
To determine the quantity of electricity required, we must identify the reduction half-reaction occurring at the cathode for the molten salt $CaCl_{2}$. Calcium exists as $Ca^{2+}$ ions in the melt. The reduction reaction is:
$Ca^{2+} (l) + 2e^{-} \rightarrow Ca (s)$
[Per Faraday's First Law of Electrolysis, the amount of substance deposited is directly proportional to the amount of electricity passed through the electrolyte.]
The molar mass of Calcium ($Ca$) is approximately $40.0 \, \text{g/mol}$.
From the balanced chemical equation, $1 \, \text{mol}$ of $Ca$ requires $2 \, \text{moles}$ of electrons ($2 \, \text{Faradays}$ of electricity) for its reduction.
Therefore:
We are given that the mass of Calcium to be produced is $20.0 \, \text{g}$. We set up a proportionality ratio based on the molar requirement:
$\text{Electricity required} = \left( \frac{2 \, \text{F}}{40.0 \, \text{g}} \right) \times 20.0 \, \text{g}$
Performing the algebraic simplification:
$\text{Electricity required} = \frac{2 \times 20.0}{40.0} \, \text{F}$
$\text{Electricity required} = \frac{40.0}{40.0} \, \text{F}$
$\text{Electricity required} = 1.0 \, \text{F}$
| Variable | Value |
|---|---|
| Molar Mass of Ca | $40.0 \, \text{g/mol}$ |
| n-factor (electrons) | $2$ |
| Mass produced | $20.0 \, \text{g}$ |
| Result | $1.0 \, \text{F}$ |
Final Solution: The amount of electricity required to produce 20.0 g of Calcium from molten $CaCl_{2}$ is 1.0 Faraday.
Solution:
In an aqueous solution of copper(II) chloride ($CuCl_2$), the following dissociation occurs:
$CuCl_2(aq) \rightarrow Cu^{2+}(aq) + 2Cl^{-}(aq)$
Additionally, since the solvent is water, we must account for the self-ionization of water:
$H_2O(l) \rightleftharpoons H^+(aq) + OH^{-}(aq)$
The ions present in the electrolyte are: $Cu^{2+}$, $Cl^{-}$, $H^+$, and $OH^{-}$.
At the cathode, reduction occurs. Two species compete for reduction:
At the anode, oxidation occurs. Two species compete for oxidation:
| Electrode | Product | Half-Reaction |
|---|---|---|
| Cathode (-) | Copper metal ($Cu$) | $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$ |
| Anode (+) | Chlorine gas ($Cl_2$) | $2Cl^-(aq) \rightarrow Cl_2(g) + 2e^-$ |
Final Solution: The product at the cathode is metallic Copper ($Cu$), and the product at the anode is Chlorine gas ($Cl_2$).
Solution:
The electrolytic reduction of molten aluminum oxide ($Al_{2}O_{3}$) involves the reduction of aluminum ions ($Al^{3+}$) to metallic aluminum ($Al$). The half-reaction occurring at the cathode is:
$Al^{3+} (melt) + 3e^{-} \rightarrow Al (s)$
[Per the definition of electrolytic reduction in Hall-Héroult process]
From the balanced half-reaction, it is evident that $1$ mole of $Al$ requires $3$ moles of electrons ($e^{-}$).
Given the mass of aluminum required is $40.0\ g$, we calculate the number of moles ($n$) using the formula $n = \frac{mass}{Molar\ mass}$:
$n(Al) = \frac{40.0\ g}{27.0\ g/mol} \approx 1.4815\ mol$
To find the total charge ($Q$) in Faraday, we multiply the number of moles of $Al$ by the charge required per mole of $Al$:
$Q = n(Al) \times 3\ F/mol$
$Q = 1.4815\ mol \times 3\ F/mol$
$Q = 4.4445\ F$
| Parameter | Value |
|---|---|
| Mass of $Al$ | $40.0\ g$ |
| Molar Mass of $Al$ | $27.0\ g/mol$ |
| Electrons per $Al$ atom | $3$ |
| Total Charge ($F$) | $4.44\ F$ |
Final Solution: The amount of electricity required to produce 40.0 g of Al from molten $Al_{2}O_{3}$ is 4.44 Faraday.
Solution:
Based on the cell notation $Mg(s)|Mg^{2+}(0.001 M)||Cu^{2+}(0.0001 M)|Cu(s)$, the anodic (oxidation) and cathodic (reduction) processes are defined as follows:
[Per the IUPAC convention for electrochemical cell representation, the oxidation half-cell is on the left and reduction half-cell is on the right.]
Using standard electrode potential values ($E^{\circ}_{Mg^{2+}/Mg} = -2.37 V$ and $E^{\circ}_{Cu^{2+}/Cu} = +0.34 V$):
$E^{\circ}_{cell} = E^{\circ}_{cathode} - E^{\circ}_{anode}$
$E^{\circ}_{cell} = 0.34 V - (-2.37 V) = 2.71 V$
The Nernst equation at $T = 298 K$ is given by:
$E_{cell} = E^{\circ}_{cell} - \frac{0.0591}{n} \log Q$
Where:
[Justification: The reaction quotient $Q$ includes only aqueous ionic species; solids have unit activity.]
Substitute the identified values into the Nernst equation:
$E_{cell} = 2.71 - \frac{0.0591}{2} \log(10)$
Since $\log(10) = 1$:
$E_{cell} = 2.71 - 0.02955 \times 1$
$E_{cell} = 2.68045 V$
The Nernst equation for the given reaction is: $E_{cell} = 2.71 - 0.02955 \log \frac{[Mg^{2+}]}{[Cu^{2+}]}$
Final Solution: The emf of the cell is 2.68 V
Solution:
The given overall chemical reaction is: $Zn(s) + 2Ag^{+}(aq) \rightarrow Zn^{2+}(aq) + 2Ag(s)$
We decompose this into two half-reactions based on the oxidation state changes [Per the definition of Redox Reactions]:
According to the IUPAC convention for cell notation, the anode is written on the left and the cathode on the right, separated by a salt bridge (denoted by $||$). Phase boundaries are represented by a vertical line ($|$).
Cell Representation: $Zn(s) \mid Zn^{2+}(aq) \parallel Ag^{+}(aq) \mid Ag(s)$
| Electrode | Reaction | Process |
|---|---|---|
| Anode | $Zn(s) \rightarrow Zn^{2+}(aq) + 2e^{-}$ | Oxidation |
| Cathode | $Ag^{+}(aq) + e^{-} \rightarrow Ag(s)$ | Reduction |
Note: The reduction reaction at the cathode is multiplied by 2 to balance the electrons transferred [Per the Law of Conservation of Mass and Charge].
Final Solution: The galvanic cell is represented as $Zn(s) \mid Zn^{2+}(aq) \parallel Ag^{+}(aq) \mid Ag(s)$. The anodic reaction is $Zn(s) \rightarrow Zn^{2+}(aq) + 2e^{-}$ and the cathodic reaction is $2Ag^{+}(aq) + 2e^{-} \rightarrow 2Ag(s)$.
Solution:
The electrolytic reduction of molten calcium chloride ($CaCl_2$) involves the reduction of calcium ions ($Ca^{2+}$) at the cathode to form metallic calcium ($Ca$).
The half-cell reaction at the cathode is:
$Ca^{2+}(l) + 2e^- \rightarrow Ca(s)$
[Per the definition of electrolytic reduction, the charge required to reduce 1 mole of a metal ion is equal to $n \times F$, where $n$ is the valency of the metal and $F$ is Faraday's constant.]
The atomic mass of Calcium ($Ca$) is approximately $40.0 \, g/mol$.
From the balanced half-reaction, it is evident that:
Using the unitary method, we determine the amount of Faraday ($F$) required to produce $20.0 \, g$ of $Ca$:
$\text{Electricity required} = \left( \frac{2 \, F}{40.0 \, g} \right) \times 20.0 \, g$
[By the Principle of Stoichiometric Equivalence]
$\text{Electricity required} = \frac{2}{40.0} \times 20.0 \, F$
$\text{Electricity required} = 0.05 \times 20.0 \, F = 1.0 \, F$
| Parameter | Value |
|---|---|
| Target Mass of Ca | $20.0 \, g$ |
| Molar Mass of Ca | $40.0 \, g/mol$ |
| Moles of Ca produced | $0.5 \, mol$ |
| Faraday Required | $1.0 \, F$ |
Final Solution: The amount of electricity required to produce 20.0 g of Calcium from molten $CaCl_2$ is 1.0 Faraday.
Solution:
To determine the feasibility of the reaction between $Ag^{+}(aq)$ and $Cu(s)$, we must define the oxidation and reduction half-reactions. The overall spontaneous reaction occurs if the cell potential ($E^{\circ}_{cell}$) is positive [Per the Nernst Equation and Gibbs Free Energy relationship $\Delta G^{\circ} = -nFE^{\circ}_{cell}$].
Based on the electrochemical series (standard reduction potentials at $298 \, K$):
| Half-Reaction | $E^{\circ}$ (Volts) |
|---|---|
| $Ag^{+}(aq) + e^{-} \rightarrow Ag(s)$ | $+0.80 \, V$ |
| $Cu^{2+}(aq) + 2e^{-} \rightarrow Cu(s)$ | $+0.34 \, V$ |
The standard cell potential is calculated using the formula: $E^{\circ}_{cell} = E^{\circ}_{cathode} - E^{\circ}_{anode}$ [By Definition of Electrochemical Cell Potential].
Substituting the values:
$E^{\circ}_{cell} = E^{\circ}_{Ag^{+}/Ag} - E^{\circ}_{Cu^{2+}/Cu}$
$E^{\circ}_{cell} = 0.80 \, V - 0.34 \, V$
$E^{\circ}_{cell} = +0.46 \, V$
A reaction is considered feasible if the change in Gibbs Free Energy ($\Delta G^{\circ}$) is negative. Since $\Delta G^{\circ} = -nFE^{\circ}_{cell}$, a positive $E^{\circ}_{cell}$ results in a negative $\Delta G^{\circ}$ [Per the Second Law of Thermodynamics regarding spontaneity].
Since $E^{\circ}_{cell} = +0.46 \, V > 0$, the reaction is spontaneous and therefore feasible.
Final Solution: The reaction between $Ag^{+}(aq)$ and $Cu(s)$ is feasible because the calculated standard cell potential ($E^{\circ}_{cell}$) is $+0.46 \, V$, which is greater than zero, indicating a spontaneous process.
Solution:
In an aqueous solution of silver nitrate ($AgNO_{3}$), the substance dissociates completely according to the following equation: $AgNO_{3}(aq) \rightarrow Ag^{+}(aq) + NO_{3}^{-}(aq)$
Since it is an aqueous solution, water ($H_{2}O$) molecules are also present, which can undergo oxidation or reduction [Per the Nernst Theory of Electrolytic Dissociation].
At the electrodes, the species with higher reduction potential (for cathode) or lower oxidation potential (for anode) will preferentially react. Because silver electrodes are used, the electrodes are active, meaning they participate in the reaction.
At the Cathode (Reduction):
Since the reduction potential of $Ag^{+}$ is significantly higher than that of $H_{2}O$ [Per the Electrochemical Series], $Ag^{+}$ ions are preferentially reduced to metallic silver.
At the Anode (Oxidation):
In the presence of an active silver anode, the silver metal itself is more easily oxidized than the water or the nitrate ions [Per the Principle of Preferential Discharge]. Therefore, the anode undergoes dissolution.
As the current flows through the circuit:
Effectively, the net result is the transfer of silver from the anode to the cathode.
Final Solution: The product at the cathode is metallic silver ($Ag$), and the product at the anode is the dissolution of the silver electrode (formation of $Ag^{+}$ ions in the solution).
Solution:
To determine the standard cell potential ($E^\circ_{cell}$), we identify the oxidation and reduction half-reactions:
[Per standard electrochemical data, $E^\circ_{Fe^{3+}/Fe^{2+}} = 0.77 \text{ V}$ and $E^\circ_{Ag^{+}/Ag} = 0.80 \text{ V}$]
The standard cell potential is calculated using the formula: $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$
$E^\circ_{cell} = 0.80 \text{ V} - 0.77 \text{ V} = 0.03 \text{ V}$
The relationship between $\Delta_{r}G^\circ$ and $E^\circ_{cell}$ is defined as: $\Delta_{r}G^\circ = -nFE^\circ_{cell}$
$\Delta_{r}G^\circ = -(1) \times (96500 \text{ C mol}^{-1}) \times (0.03 \text{ J C}^{-1})$
$\Delta_{r}G^\circ = -2895 \text{ J mol}^{-1} = -2.895 \text{ kJ mol}^{-1}$
Using the Nernst relationship at equilibrium: $\Delta_{r}G^\circ = -RT \ln K_c$ or $E^\circ_{cell} = \frac{0.0591}{n} \log K_c$ (at $298 \text{ K}$):
$0.03 = \frac{0.0591}{1} \log K_c$
$\log K_c = \frac{0.03}{0.0591} \approx 0.5076$
$K_c = \text{antilog}(0.5076) \approx 3.22$
Final Solution: The standard cell potential $E^\circ_{cell}$ is $0.03 \text{ V}$, the standard Gibbs energy change $\Delta_{r}G^\circ$ is $-2.895 \text{ kJ mol}^{-1}$, and the equilibrium constant $K_c$ is approximately $3.22$.
Solution:
In an aqueous dilute solution of sulfuric acid ($H_{2}SO_{4}$), the following dissociation and ionization processes occur:
The ions present in the electrolytic cell are: $H^{+}$, $SO_{4}^{2-}$, and $OH^{-}$. [Per the Arrhenius theory of dissociation].
At the cathode, reduction occurs. The competing species are $H^{+}$ ions and $H_{2}O$ molecules. Since only $H^{+}$ ions are present (from the acid), the following reduction half-reaction occurs:
$H^{+}(aq) + e^{-} \rightarrow \frac{1}{2}H_{2}(g)$
Product at Cathode: Hydrogen gas ($H_{2}$). [By standard electrode potential convention, $E^{\circ}_{H^{+}/H_{2}} = 0.00 \, V$].
At the anode, oxidation occurs. The competing species are $SO_{4}^{2-}$ and $OH^{-}$ (from water). The competing half-reactions are:
| Reaction | $E^{\circ}$ (Volts) |
|---|---|
| $2SO_{4}^{2-}(aq) \rightarrow S_{2}O_{8}^{2-}(aq) + 2e^{-}$ | $+2.01 \, V$ |
| $2H_{2}O(l) \rightarrow O_{2}(g) + 4H^{+}(aq) + 4e^{-}$ | $+1.23 \, V$ |
[Per the principle of selective discharge, the ion/molecule with the lower oxidation potential (or higher reduction potential) is preferred]. Since $E^{\circ}_{ox}$ for water ($+1.23 \, V$) is significantly lower than that of the sulfate ion ($+2.01 \, V$), water is preferentially oxidized.
The net cell reaction is the electrolysis of water:
$2H_{2}O(l) \xrightarrow{electricity} 2H_{2}(g) + O_{2}(g)$
Final Solution: The product at the cathode is Hydrogen gas ($H_{2}$) and the product at the anode is Oxygen gas ($O_{2}$).
Solution:
The given redox reaction is: $2Cr(s) + 3Cd^{2+}(aq) \rightarrow 2Cr^{3+}(aq) + 3Cd(s)$.
[Per the Nernstian standard convention, $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$]
$E^\circ_{cell} = E^\circ_{Cd^{2+}/Cd} - E^\circ_{Cr^{3+}/Cr}$
$E^\circ_{cell} = -0.40\text{ V} - (-0.74\text{ V}) = +0.34\text{ V}$
The total number of electrons transferred ($n$) in the balanced equation is $6$.
The formula for Gibbs energy is $\Delta_r G^\circ = -nFE^\circ_{cell}$, where $F = 96487\text{ C mol}^{-1}$.
$\Delta_r G^\circ = -(6) \times (96487\text{ C mol}^{-1}) \times (0.34\text{ J C}^{-1})$
$\Delta_r G^\circ = -196833.48\text{ J mol}^{-1} \approx -196.83\text{ kJ mol}^{-1}$
The relationship between $\Delta_r G^\circ$ and $K_c$ is defined by: $\Delta_r G^\circ = -RT \ln K_c$ or $\log K_c = \frac{nE^\circ_{cell}}{0.0591}$ at $298\text{ K}$.
$\log K_c = \frac{6 \times 0.34}{0.0591} = \frac{2.04}{0.0591} \approx 34.5178$
$K_c = \text{antilog}(34.5178) = 3.29 \times 10^{34}$
Final Solution: The standard cell potential $E^\circ_{cell} = +0.34\text{ V}$, the standard Gibbs free energy change $\Delta_r G^\circ = -196.83\text{ kJ mol}^{-1}$, and the equilibrium constant $K_c = 3.29 \times 10^{34}$.
Solution:
In an aqueous solution of silver nitrate ($AgNO_{3}$), the following ions are present:
[Per the principle of electrolytic dissociation in aqueous media].
At the cathode, reduction occurs. The competing reactions are:
Since the standard electrode potential ($E^{\circ}$) for the reduction of $Ag^{+}$ is significantly higher (more positive) than that of water, $Ag^{+}$ ions will be preferentially reduced at the cathode [Per the Electrochemical Series hierarchy].
Because the electrodes are specified as Silver (Ag), the anode is active. In cells with active metallic electrodes, the electrode material itself undergoes oxidation if its oxidation potential is higher than that of the anions or water.
The competing reactions are:
Since the oxidation potential of silver ($+0.80 \, V$) is greater than that of water ($-1.23 \, V$), the silver anode will dissolve into the solution [Per the Selective Discharge Theory for active electrodes].
| Electrode | Product | Reaction |
|---|---|---|
| Cathode | Silver metal ($Ag$) | $Ag^{+} + e^{-} \rightarrow Ag$ |
| Anode | Silver ions ($Ag^{+}$) | $Ag \rightarrow Ag^{+} + e^{-}$ |
Final Solution: The product at the cathode is the deposition of metallic silver ($Ag$), and the product at the anode is the dissolution of the silver electrode into the solution as silver ions ($Ag^{+}$).
Solution:
To determine the feasibility of the reaction between $Fe^{3+}(aq)$ and $I^{-}(aq)$, we must evaluate the standard Gibbs free energy change ($\Delta G^\circ$) or the standard cell potential ($E^\circ_{cell}$). The spontaneous reaction occurs if $E^\circ_{cell} > 0$.
Based on standard electrochemical data (Table 3.1):
For a spontaneous reaction to occur, the species with the higher reduction potential must act as the cathode (undergo reduction), and the species with the lower reduction potential must act as the anode (undergo oxidation). [Per the Nernstian electrochemical framework].
| Species | $E^\circ$ Value | Role |
|---|---|---|
| $Fe^{3+}/Fe^{2+}$ | $+0.77 \text{ V}$ | Cathode (Reduction) |
| $I_2/I^-$ | $+0.54 \text{ V}$ | Anode (Oxidation) |
The proposed reaction is the oxidation of iodide ions by iron(III) ions:
Cathode (Reduction): $2Fe^{3+}(aq) + 2e^- \rightarrow 2Fe^{2+}(aq)$
Anode (Oxidation): $2I^{-}(aq) \rightarrow I_2(s) + 2e^-$
Overall Cell Reaction: $2Fe^{3+}(aq) + 2I^{-}(aq) \rightarrow 2Fe^{2+}(aq) + I_2(s)$
The standard cell potential is calculated using the formula: $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$ [By the IUPAC convention for electromotive force].
$E^\circ_{cell} = E^\circ_{Fe^{3+}/Fe^{2+}} - E^\circ_{I_2/I^-}$
$E^\circ_{cell} = 0.77 \text{ V} - 0.54 \text{ V}$
$E^\circ_{cell} = +0.23 \text{ V}$
Since the calculated $E^\circ_{cell}$ is positive ($+0.23 \text{ V}$), the standard Gibbs free energy change $\Delta G^\circ$ is negative, as determined by the relation $\Delta G^\circ = -nFE^\circ_{cell}$ [Per the Thermodynamic Criterion for Spontaneity].
Final Solution: The reaction $2Fe^{3+}(aq) + 2I^{-}(aq) \rightarrow 2Fe^{2+}(aq) + I_2(s)$ is feasible because the standard cell potential $E^\circ_{cell}$ is positive (+0.23 V).
Solution:
The overall cell reaction is: $Fe^{2+}(aq) + Ag^{+}(aq) \rightarrow Fe^{3+}(aq) + Ag(s)$.
We split the reaction into oxidation and reduction half-cells:
[Per the standard electrode potential table values at 298 K]
The standard cell potential is calculated using the formula: $E^{\circ}_{cell} = E^{\circ}_{cathode} - E^{\circ}_{anode}$.
$E^{\circ}_{cell} = 0.80 \, V - 0.77 \, V = 0.03 \, V$
The Gibbs energy change is given by $\Delta_{r}G^{\circ} = -nFE^{\circ}_{cell}$, where $n$ is the number of electrons transferred, $F$ is Faraday's constant ($96487 \, C \, mol^{-1}$), and $E^{\circ}_{cell} = 0.03 \, V$.
Here, $n = 1$.
$\Delta_{r}G^{\circ} = -(1) \times (96487 \, C \, mol^{-1}) \times (0.03 \, V)$
$\Delta_{r}G^{\circ} = -2894.61 \, J \, mol^{-1} \approx -2.89 \, kJ \, mol^{-1}$
[By the fundamental relationship between thermodynamics and electrochemistry]
The relationship between equilibrium constant and cell potential is defined as: $\Delta_{r}G^{\circ} = -RT \ln K_c$, or equivalently, $E^{\circ}_{cell} = \frac{0.0591}{n} \log K_c$ at 298 K.
$0.03 = \frac{0.0591}{1} \log K_c$
$\log K_c = \frac{0.03}{0.0591} \approx 0.5076$
$K_c = \text{antilog}(0.5076) = 10^{0.5076} \approx 3.22$
| Parameter | Calculated Value |
|---|---|
| $E^{\circ}_{cell}$ | $0.03 \, V$ |
| $\Delta_{r}G^{\circ}$ | $-2.89 \, kJ \, mol^{-1}$ |
| $K_c$ | $3.22$ |
Final Solution: The standard cell potential is $0.03 \, V$, the standard Gibbs free energy change is $-2.89 \, kJ \, mol^{-1}$, and the equilibrium constant $K_c$ is $3.22$.
Solution:
To calculate the molar conductivity ($\Lambda_m$) for a given solution, we utilize the following fundamental relationship:
$\Lambda_m = \frac{\kappa}{c} \times 1000$
Where:
Using the provided data points, we calculate $\Lambda_m$ and $\sqrt{c}$ (in $(mol \cdot L^{-1})^{1/2}$):
| $c (mol \cdot L^{-1})$ | $\kappa (S \cdot cm^{-1})$ | $\sqrt{c} (mol^{1/2} \cdot L^{-1/2})$ | $\Lambda_m (S \cdot cm^2 \cdot mol^{-1})$ |
|---|---|---|---|
| 0.001 | $1.237 \times 10^{-4}$ | 0.0316 | 123.7 |
| 0.010 | $1.185 \times 10^{-3}$ | 0.1000 | 118.5 |
| 0.020 | $2.315 \times 10^{-3}$ | 0.1414 | 115.75 |
| 0.050 | $5.553 \times 10^{-3}$ | 0.2236 | 111.06 |
| 0.100 | $1.067 \times 10^{-2}$ | 0.3162 | 106.7 |
The relationship is governed by the Debye-Hückel-Onsager equation:
$\Lambda_m = \Lambda^0_m - A\sqrt{c}$
By plotting $\Lambda_m$ vs $\sqrt{c}$ and extrapolating the linear regression to the y-intercept (where $\sqrt{c} = 0$), we obtain the value for the molar conductivity at infinite dilution.
Based on the calculated slope $m \approx -58.05$ and the trend line passing through the data points:
$\Lambda^0_m \approx 124.0 \, S \cdot cm^2 \cdot mol^{-1}$
Final Solution: The calculated molar conductivity values are [123.7, 118.5, 115.75, 111.06, 106.7] $S \cdot cm^2 \cdot mol^{-1}$ respectively. The extrapolated molar conductivity at infinite dilution $\Lambda^0_m$ is 124.0 $S \cdot cm^2 \cdot mol^{-1}$.
Solution:
Based on the cell notation $Mg(s)|Mg^{2+}(0.001M)||Cu^{2+}(0.0001 M)|Cu(s)$, the electrochemical cell consists of an oxidation half-cell (anode) and a reduction half-cell (cathode).
[Per the convention of electrochemical cell notation, the anode is written on the left and the cathode on the right]. The number of electrons involved in the transfer process is $n = 2$.
The standard reduction potentials for the electrodes are:
The standard cell potential is calculated as:
$E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$
$E^\circ_{cell} = 0.34 \, V - (-2.37 \, V) = 2.71 \, V$
The Nernst equation for the cell at $298 \, K$ is given by:
$E_{cell} = E^\circ_{cell} - \frac{0.0591}{n} \log \frac{[Mg^{2+}]}{[Cu^{2+}]}$
[By the Nernst Equation definition, where $Q = \frac{[Product]}{[Reactant]}$ and considering pure solids have unit activity].
Substituting the given concentrations: $[Mg^{2+}] = 10^{-3} \, M$ and $[Cu^{2+}] = 10^{-4} \, M$
$E_{cell} = 2.71 - \frac{0.0591}{2} \log \frac{10^{-3}}{10^{-4}}$
$E_{cell} = 2.71 - 0.02955 \log(10)$
Since $\log(10) = 1$:
$E_{cell} = 2.71 - 0.02955$
$E_{cell} = 2.68045 \, V$
Final Solution: The Nernst equation is $E_{cell} = 2.71 - \frac{0.0591}{2} \log \frac{[Mg^{2+}]}{[Cu^{2+}]}$ and the emf of the cell is $2.68 \, V$ (approx).
Solution:
According to [Faraday’s First Law of Electrolysis], the mass ($m$) of a substance deposited at an electrode is directly proportional to the quantity of electricity ($Q$) passed through the electrolyte: $m = ZIt = \frac{MIt}{nF}$, where $M$ is the molar mass, $I$ is current in Amperes, $t$ is time in seconds, $n$ is the number of moles of electrons involved, and $F$ is Faraday’s constant ($\approx 96487 \, C \, mol^{-1}$).
For cell B ($AgNO_{3}$), the cathodic reaction is: $Ag^+ + e^- \rightarrow Ag(s)$. Here, $n = 1$.
Rearranging the formula for time ($t$):
$t = \frac{m_{Ag} \times n \times F}{M_{Ag} \times I} = \frac{1.45 \, g \times 1 \times 96487 \, C \, mol^{-1}}{107.87 \, g \, mol^{-1} \times 1.5 \, A}$
$t = \frac{139906.15}{161.805} \approx 864.66 \, s$
For cell C ($CuSO_{4}$), the cathodic reaction is: $Cu^{2+} + 2e^- \rightarrow Cu(s)$. Here, $n = 2$.
$m_{Cu} = \frac{M_{Cu} \times I \times t}{n \times F} = \frac{63.55 \times 1.5 \times 864.66}{2 \times 96487}$
$m_{Cu} = \frac{82424.3}{192974} \approx 0.427 \, g$
For cell A ($ZnSO_{4}$), the cathodic reaction is: $Zn^{2+} + 2e^- \rightarrow Zn(s)$. Here, $n = 2$.
$m_{Zn} = \frac{M_{Zn} \times I \times t}{n \times F} = \frac{65.38 \times 1.5 \times 864.66}{2 \times 96487}$
$m_{Zn} = \frac{84795.1}{192974} \approx 0.439 \, g$
| Substance | Mass Deposited (g) |
|---|---|
| Silver (Ag) | 1.45 |
| Copper (Cu) | 0.427 |
| Zinc (Zn) | 0.439 |
Final Solution: The current flowed for 864.66 seconds. The mass of copper deposited is 0.427 g, and the mass of zinc deposited is 0.439 g.