Electrochemistry

01

PYQ 2023

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The column of a solution of 0.05 mol L NaOH has diameter 2.0 cm and length 100 cm. The resistance of the column of solution is 5.55 10 ohm. Calculate its resistivity, conductivity and molar conductivity.

02

PYQ 2023

medium

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At 298 K write Nernst equation for the following cell - Ni Ni (0.01 M) Cu (0.1 M) Cu. If the emf of the above cell () is 0.59 V then calculate the standard emf of the cell ()

03

PYQ 2023

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$Explain Kohlrausch’s law of independent migration of ions. Mention one application of this law.$

Official Solution

Correct Option: (1)

$Step 1: Statement of Kohlrausch’s law. Kohlrausch’s law states that at infinite dilution, the molar conductivity of an electrolyte is the sum of the contributions of its individual ions. Each ion migrates independently of the other. where, = molar conductivity at infinite dilution = limiting molar conductivity of cation = limiting molar conductivity of anion Step 2: Application. It is used to calculate the molar conductivity of weak electrolytes (like acetic acid) at infinite dilution by using values of strong electrolytes. Example: Conclusion: Kohlrausch’s law helps in determining the degree of dissociation and dissociation constant of weak electrolytes.$

04

PYQ 2023

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$Write Nernst equation and its one application.$

Official Solution

Correct Option: (1)

$Step 1: General form of the Nernst equation. The Nernst equation relates the electrode potential of a half-cell to the standard electrode potential, temperature, and the activities (or concentrations) of the chemical species involved. At, the equation simplifies to: where, = electrode potential = standard electrode potential = gas constant (8.314 J K mol) = temperature (in Kelvin) = number of electrons involved in reaction = Faraday constant (96500 C mol) Step 2: One application. The Nernst equation is used to calculate the electrode potential of a cell under non-standard conditions. For example, the potential of a Daniell cell: can be calculated under different concentrations of Zn and Cu . Conclusion: The Nernst equation provides a direct relation between electrode potential and ionic concentrations, helping in predicting the feasibility and direction of redox reactions.$

05

PYQ 2023

medium

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$What is Kohlrausch law? Write its applications.$

Official Solution

Correct Option: (1)

$Step 1: Kohlrausch Law. Kohlrausch's law states that the molar conductivity of an electrolyte at infinite dilution is the sum of the molar conductivities of its individual ions. Mathematically: where is the molar conductivity at infinite dilution, and and are the molar conductivities of the cation and anion respectively. Step 2: Applications. - It is used to determine the limiting molar conductivity of ions. - It helps in calculating the conductivity of strong and weak electrolytes. - It is also used to calculate the dissociation constant of weak electrolytes.$

06

PYQ 2023

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$The resistance of a conductivity cell, filled with 0.1 mol L KCl solution is 100 . If the resistance of this cell is 500 on filling 0.02 mol L KCl solution, then calculate the conductivity and molar conductivity of 0.02 mol L KCl solution. The conductivity of 0.1 mol L KCl solution is 1.29 S m .$

Official Solution

Correct Option: (1)

$Step 1: Calculate cell constant. Conductivity () = Cell constant / Resistance. For 0.1 M KCl: Step 2: Find conductivity for 0.02 M KCl. Step 3: Find molar conductivity. Step 4: Conclusion. Conductivity =, Molar conductivity = .$

07

PYQ 2023

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$Give answers: (i) Why does the conductivity of any solution decrease with dilution? (ii) Conductivity of 0.20 M KCl solution at 298 K is 0.248 S cm . What will be its molar conductivity?$

Official Solution

Correct Option: (1)

$(i) Reason. Conductivity decreases with dilution because the number of ions per unit volume decreases, reducing total current carrying capacity. (ii) Calculation. Molar conductivity: Step 3: Conclusion. (i) Fewer ions per volume \to lower conductivity. (ii) Molar conductivity = 124 S cm mol .$

08

PYQ 2023

medium

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$Write Nernst equation and its one application in chemical cells.$

Official Solution

Correct Option: (1)

$Step 1: General form of Nernst equation. The Nernst equation relates the cell potential under non-standard conditions to the standard electrode potential and the reaction quotient: where: - = electrode potential under given conditions - = standard electrode potential - = gas constant () - = absolute temperature (in K) - = number of electrons transferred - = Faraday constant () - = reaction quotient At, the equation becomes: Step 2: Application. One application of the Nernst equation is in calculating the electrode potential of the hydrogen electrode: Thus, the Nernst equation helps determine the pH of a solution using hydrogen electrode. Conclusion: The Nernst equation is essential in electrochemistry for predicting cell potentials under non-standard conditions and is widely used in calculating pH values and electrode potentials.$

09

PYQ 2023

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$The value of standard electrode potential of Daniell cell is 1.1 V. Calculate the value of standard Gibbs energy for the following reaction.$

Official Solution

Correct Option: (1)

$Step 1: Recall the relationship between Gibbs free energy and cell potential. The formula is: where, - = number of electrons transferred in the reaction = 2 - = Faraday constant = - = standard electrode potential = Step 2: Substitute the values. Conclusion: The standard Gibbs energy for the Daniell cell reaction is:$

10

PYQ 2023

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$Explain the following: (A) Conductance, (B) Cell constant.$

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Correct Option: (1)

$Step 1: Conductance. Resistance () opposes current; conductance is ease of current flow. Step 2: Cell constant. In a conductivity cell: where = distance between electrodes, = electrode area. Step 3: Importance. Cell constant helps to convert measured conductance into specific conductance.$

11

PYQ 2023

medium

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$Unit of specific conductance is:$

1

$ohm cm mol$

2

$ohm cm mol$

3

$ohm cm mol$

4

$ohm cm mol$

Official Solution

Correct Option: (1)

$Step 1: Definition. Specific conductance (or conductivity,) is the conductance of 1 cm of a solution placed between two electrodes 1 cm apart. Step 2: Unit. Since conductance unit is ohm (or siemens, S), and length factor introduces cm, the unit is ohm cm . Step 3: Conclusion. Therefore, the unit of specific conductance is ohm cm .$

12

PYQ 2023

medium

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$Non-electrolyte is:$

1

$Sodium chloride$

2

$Urea$

3

$Ammonium nitrate$

4

$Nitric acid$

Official Solution

Correct Option: (2)

$Step 1: Understanding electrolytes. Electrolytes are substances that dissociate into ions in aqueous solution and conduct electricity. Non-electrolytes do not dissociate and hence do not conduct electricity. Step 2: Analysis of options. - Sodium chloride: Electrolyte, produces Na and Cl ions. - Urea: Non-electrolyte, dissolves in water but does not produce ions. - Ammonium nitrate: Electrolyte, dissociates into NH and NO . - Nitric acid: Strong electrolyte, ionizes completely. Step 3: Conclusion. Thus, the non-electrolyte among the options is (B) Urea.$

13

PYQ 2023

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$Calculate the standard e.m.f. of the following cell: Zn Zn Cu Cu Given: and$

Official Solution

Correct Option: (1)

$Step 1: Identify electrodes. - Oxidation occurs at the anode (Zn electrode). - Reduction occurs at the cathode (Cu electrode). Step 2: Formula for standard e.m.f. Step 3: Substitute values. Conclusion: The standard e.m.f. of the given cell is:$

14

PYQ 2023

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$What is Kohlrausch’s law? Write its one application with example.$

Official Solution

Correct Option: (1)

$Step 1: Statement of Kohlrausch’s Law. Kohlrausch’s law of independent migration of ions states that at infinite dilution, each ion makes a definite contribution to the molar conductivity of the electrolyte, independent of the other ions present. where, - = molar conductivity at infinite dilution - = contribution of cation - = contribution of anion Step 2: Application. It is used to calculate the molar conductivity of weak electrolytes at infinite dilution by using strong electrolytes. Example: For acetic acid (), which is a weak electrolyte: Conclusion: Kohlrausch’s law helps in determining dissociation constants of weak electrolytes and studying ionic conductivities.$

15

PYQ 2023

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$Unit of specific conductance is:$

Official Solution

Correct Option: (1)

$Step 1: Understanding specific conductance. Specific conductance (or conductivity,) is the conductance of 1 cm of solution placed between two electrodes of 1 cm area separated by 1 cm. Step 2: Relation of conductance and resistance. Conductance = = ohm . Since specific conductance accounts for distance (cm) and area (cm), its unit becomes: Step 3: Conclusion. Thus, the unit of specific conductance is cm ohm . Final Answer:$

16

PYQ 2024

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$Write the difference between Galvanic cell and Electrolytic cell.$

Official Solution

Correct Option: (1)

$- Galvanic Cell: Converts chemical energy into electrical energy. It has a spontaneous reaction. - Electrolytic Cell: Converts electrical energy into chemical energy. It has a non-spontaneous reaction.$

17

PYQ 2024

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$Explain molar conductivity. The resistance of a cell filled with KCl solution is . Calculate the molar conductivity of the solution. (Cell constant =).$

Official Solution

Correct Option: (1)

$Molar Conductivity (): It is the conductivity of an electrolyte solution per unit concentration: where is the conductivity and is the molarity of the solution. Calculation: 1. Conductivity (): 2. Molar conductivity ():$

18

PYQ 2024

easy

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$SI unit of (rho) is:$

Official Solution

Correct Option: (1)

19

PYQ 2024

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$After eliminating salt bridge of any Galvanic cell, voltage of the cell:$

1

$Suddenly becomes zero$

2

$Goes down slowly$

3

$increases rapidly$

4

$Remains unchanged$

Official Solution

Correct Option: (1)

$The salt bridge maintains ionic balance and completes the circuit in a galvanic cell. Removing it stops ion flow, making the cell voltage drop to zero instantly.$

20

PYQ 2024

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$Is oxidation of bromide ion into bromine by ferric ion possible?$

Official Solution

Correct Option: (1)

$The standard electrode potentials are given as: Since the reduction potential of is higher than, bromide ions cannot be oxidized by ferric ions.$

21

PYQ 2024

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$Explain the difference between an electrochemical cell and electrolytic cell. State Kohlrausch's law and write its applications.$

Official Solution

Correct Option: (1)

$Step 1: Difference Between Electrochemical and Electrolytic Cells: Feature & Electrochemical Cell & Electrolytic Cell Energy Conversion & Chemical to electrical & Electrical to chemical Spontaneity & Spontaneous reaction & Non-spontaneous reaction Example & Galvanic/Daniel cell & Electrolysis of NaCl Step 2: Kohlrausch's Law: where and are the limiting molar conductivities of cations and anions, respectively. Step 3: Applications: - Used to calculate the molar conductivity of weak electrolytes. - Helps in determining dissociation constants of weak acids and bases.$

22

PYQ 2024

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$The standard electrode potential of Daniel cell is 1.1 volt. Calculate the standard Gibbs energy for the following reaction:$

Official Solution

Correct Option: (1)

$Step 1: Gibbs free energy is related to e.m.f. using: where (electrons transferred), C/mol, and . Step 2: Calculate: Thus, the Gibbs free energy is **-212.3 kJ/mol**.$

23

PYQ 2024

medium

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$Calculate the e.m.f. of the following cell: Given:$

Official Solution

Correct Option: (1)

$Step 1: Cell Reaction: Step 2: Standard E.M.F. Calculation: Step 3: Nernst Equation: Thus, the e.m.f. of the cell is 2.65V.$

24

PYQ 2024

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$What are fuel cells? State Two advantages of hydrogen-oxygen fuel cell over ordinary cell.$

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Correct Option: (1)

$Step 1: Definition of Fuel Cells: Fuel cells are electrochemical devices that convert chemical energy into electrical energy through a redox reaction between fuel (e.g., hydrogen) and an oxidizing agent (e.g., oxygen). Step 2: Advantages of Hydrogen-Oxygen Fuel Cell: 1. Higher Efficiency: Fuel cells have higher efficiency compared to conventional electrochemical cells. 2. Eco-friendly: Produces only water as a byproduct, making it environmentally friendly.$

25

PYQ 2025

easy

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$A cell in which the following reaction occurs: has standard electrode potential at . Calculate the standard Gibbs energy and the equilibrium constant of the cell reaction.$

Official Solution

Correct Option: (1)

$For a galvanic cell at standard state, and . Hence, . Given: . Overall reaction involves transfer of electrons. Step 1: Calculate standard Gibbs energy change. Step 2: Calculate equilibrium constant. Answer: .$

26

PYQ 2025

hard

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$Explain in brief the Faraday's laws of Electrolysis. CuSO solution was electrolysed for 20 minutes with 2.0 ampere current. What will be the mass of precipitated copper at cathode?$

Official Solution

Correct Option: (1)

$Faraday's First Law: The mass of a substance liberated (or deposited) at an electrode is directly proportional to the total electric charge passed through the electrolyte. where is mass deposited, is charge, and is the electrochemical equivalent. Faraday's Second Law: When the same quantity of electricity is passed through different electrolytes, the masses of substances deposited are proportional to their chemical (equivalent) weights. Numerical Part: In CuSO electrolysis, copper is deposited by For a metal ion requiring electrons, where,,,, .$

27

PYQ 2025

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$What is Kohlrausch law? Write its two applications.$

Official Solution

Correct Option: (1)

$Statement of Kohlrausch's Law: At infinite dilution, the molar conductivity of an electrolyte is equal to the sum of the contributions of its individual ions. where and are the limiting molar conductivities of cations and anions respectively. Applications: 1. To calculate the molar conductivity of weak electrolytes at infinite dilution (since they cannot be measured directly). 2. To determine the degree of dissociation () and dissociation constant () of weak electrolytes.$

28

PYQ 2025

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$What is Nernst equation? Write the relation between standard electrode potential and electrode potential.$

Official Solution

Correct Option: (1)

$The Nernst equation gives the relation between electrode potential and the concentrations (activities) of the ions involved in the electrode reaction. For a general half-cell reaction: The Nernst equation is: or equivalently, Relation: - = standard electrode potential (when ion concentration is 1 M). - = electrode potential under given conditions. Thus, electrode potential depends on concentration, number of electrons transferred, and temperature. where = reaction quotient.$

29

PYQ 2025

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$Explain molar conductivity. The resistance of a cell filled with 0.02 mol L KCl solution is 480 . Calculate the molar conductivity of the solution. (Cell constant = 1.29 cm).}$

Official Solution

Correct Option: (1)

$Definition: Molar conductivity is the conductance of all the ions produced by 1 mole of electrolyte placed between two electrodes 1 cm apart, with the solution having unit cross-sectional area. It is given by, where is conductivity (S cm) and is concentration in mol L . Step 1: Find conductivity . Conductance . Step 2: Calculate molar conductivity. .$

30

PYQ 2025

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$What is electrode potential? Mention the factors affecting it.$

Official Solution

Correct Option: (1)

$Definition: Electrode potential is the potential difference developed between a metal electrode and its electrolyte solution when the electrode is in equilibrium with its ions. It represents the tendency of the electrode to lose or gain electrons. Factors affecting electrode potential: 1. Nature of metal: Different metals have different tendencies to lose or gain electrons, hence different electrode potentials. 2. Concentration of ions: The concentration of metal ions in solution affects electrode potential according to the Nernst equation. 3. Temperature: Electrode potential varies with temperature as it affects the movement of ions. 4. Pressure of gas (if involved): For electrodes involving gases (like hydrogen electrode), the gas pressure influences the electrode potential. Thus, electrode potential is not fixed, but depends on these experimental conditions.$

31

PYQ 2025

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$Explain Faraday's laws of electrolysis.$

Official Solution

Correct Option: (1)

$First Law (Mass-Charge law): The mass of a substance liberated (or deposited) at an electrode is directly proportional to the quantity of electricity passed through the electrolyte. where is current in ampere, is time in seconds, and is the electrochemical equivalent (g C). Second Law (Equivalent-Weight law): When the same quantity of electricity passes through different electrolytes, the masses of substances liberated are proportional to their chemical (equivalent) weights. where is molar mass and is the electrons transferred per ion (valency). Equivalently, for a given substance: with (Faraday constant).$

32

PYQ 2025

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$Explain Kohlrausch Law. Limiting molar conductances () of and ions in water at 298 K are 119.0 S cm mol and 76.3 S cm mol respectively. Calculate of .$

Official Solution

Correct Option: (1)

$Kohlrausch's Law: Kohlrausch's Law of limiting molar conductivity states that the limiting molar conductivity of an electrolyte is the sum of the limiting molar conductances of the individual ions that make up the electrolyte. Mathematically, it is expressed as: Where: - is the limiting molar conductivity of the electrolyte, - is the limiting molar conductivity of the cation, - is the limiting molar conductivity of the anion. For, the cation is and the anion is . From the given data: -, - . Using Kohlrausch's Law: Substituting the values: Thus, the limiting molar conductivity of is 195.3 S cm mol .$

33

PYQ 2025

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$Why do the conductivity of a solution decreases with dilution? Explain with reason.$

Official Solution

Correct Option: (1)

$Effect of Dilution on Conductivity: The conductivity of a solution decreases with dilution because as the solution is diluted, the number of ions in the solution per unit volume decreases. This leads to a decrease in the overall current-carrying capacity of the solution. The key factors involved are: 1. Ion Concentration: Conductivity () of a solution depends on the concentration of ions. As the concentration of ions decreases with dilution, the conductivity also decreases. The relationship is given by: Where: - is the conductivity, - is the concentration of the ion, - is the molar conductivity of the ion. As dilution decreases the concentration, the conductivity decreases as well. 2. Ion Pairing: At higher concentrations, ions tend to form ion pairs, which reduce the number of free ions in the solution, thus decreasing the conductivity. When a solution is diluted, ion pairing is minimized, but the total number of free ions decreases due to the lower concentration. 3. Decrease in Collision Frequency: In concentrated solutions, ions are closer to each other and collide more often, which increases the chances of electrical conduction. As the solution is diluted, the ions are further apart, leading to fewer collisions and lower conductivity. Thus, with dilution, the total ion concentration and the ion mobility decrease, leading to a reduction in the overall conductivity of the solution.$

34

PYQ 2025

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$The resistance of a column formed by a 0.10 mol L^{-1} concentrated solution is 6.5 × 10^3 ohm. Its diameter is 1 cm and length is 50 cm. Calculate its resistivity, conductivity and molar conductivity.$

Official Solution

Correct Option: (1)

$The formula for resistance of a solution is given by: Where: - is the resistance, - is the resistivity, - is the length of the column, - is the cross-sectional area of the column. We are given: - Resistance, - Length, - Diameter, Step 1: Calculate the cross-sectional area. The cross-sectional area of the column is given by the area of a circle: Step 2: Calculate the resistivity. Rearranging the formula for resistance, we can solve for resistivity: Thus, the resistivity is . Step 3: Calculate the conductivity. Conductivity is the reciprocal of resistivity: Thus, the conductivity is . Step 4: Calculate the molar conductivity. Molar conductivity is given by: Where: - is the conductivity, - is the concentration of the solution in mol/L. Given, we can calculate the molar conductivity: Thus, the molar conductivity is .$

35

PYQ 2025

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$Calculate the electromotive force of the following cell: Given,$

Official Solution

Correct Option: (1)

$Step 1: Write the Nernst equation The Nernst equation for a cell is given by: where: - is the electromotive force (EMF) of the cell, - is the standard cell potential, - is the number of electrons involved, - is the reaction quotient. Step 2: Standard Cell Potential The standard cell potential is: Since the reduction half-reaction occurs at the cathode and the oxidation half-reaction occurs at the anode: - Step 3: Calculate the Electromotive Force Since both solutions are 1M, the reaction quotient, and hence the log term becomes zero. Therefore, the electromotive force is equal to the standard cell potential: Final Answer: The electromotive force of the cell is . Correct Answer: 0.46V$

36

PYQ 2026

medium

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$Write the definition of electrode potential and cell electromotive force (emf).$

Official Solution

Correct Option: (1)

$1. Electrode Potential: When a metal rod is dipped into a solution of its own ions, a potential difference develops at the interface between the metal electrode and the electrolyte (solution). This potential difference is called the Electrode Potential. If the metal has a tendency to oxidize (lose electrons), it is Oxidation Potential. If metal ions have a tendency to reduce (gain electrons), it is Reduction Potential. 2. Cell Electromotive Force (emf): The electromotive force (emf) of a cell is the potential difference between the two electrodes of a galvanic cell when no current is drawn from the cell (open circuit). It is the maximum voltage the cell can deliver.$

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Electrochemistry

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Chapter Questions 36 MCQs

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Chapter Questions
36 MCQs