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Chemistry Part 1

Electrochemistry

Electrochemistry

Action PlanNotesQuestionsMock-Test
Study Action Plan (Sorted by Difficulty)
Ionic and Electronic Conductance
Accuracy: 35%
Total Attempted20
Total Correct7
Total Incorrect13
Difficulty Level:
High
Conductivity and Molar Conductivity
Accuracy: 36%
Total Attempted72
Total Correct26
Total Incorrect46
Difficulty Level:
High
Variation of Conductivity for Strong and Weak Electrolytes
Accuracy: 37%
Total Attempted142
Total Correct53
Total Incorrect89
Difficulty Level:
High
Degree of Dissociation and Dissociation Constant from Conductance
Accuracy: 38%
Total Attempted21
Total Correct8
Total Incorrect13
Difficulty Level:
High
Electrolysis Products
Accuracy: 45%
Total Attempted102
Total Correct46
Total Incorrect56
Difficulty Level:
High
Galvanic Cell Representation and Cell Potential
Accuracy: 45%
Total Attempted75
Total Correct34
Total Incorrect41
Difficulty Level:
High
Fuel Cells
Accuracy: 48%
Total Attempted79
Total Correct38
Total Incorrect41
Difficulty Level:
High
Nernst Equation
Accuracy: 49%
Total Attempted98
Total Correct48
Total Incorrect50
Difficulty Level:
High
Electrochemical Cells
Accuracy: 51%
Total Attempted135
Total Correct69
Total Incorrect66
Difficulty Level:
Medium
Corrosion as an Electrochemical Process
Accuracy: 52%
Total Attempted95
Total Correct49
Total Incorrect46
Difficulty Level:
Medium
Kohlrausch's Law
Accuracy: 54%
Total Attempted90
Total Correct49
Total Incorrect41
Difficulty Level:
Medium
Electrochemical Cell, Gibbs Energy and Equilibrium Constant
Accuracy: 57%
Total Attempted60
Total Correct34
Total Incorrect26
Difficulty Level:
Medium
Faraday's Laws of Electrolysis
Accuracy: 63%
Total Attempted67
Total Correct42
Total Incorrect25
Difficulty Level:
Medium
Primary and Secondary Batteries
Accuracy: 63%
Total Attempted41
Total Correct26
Total Incorrect15
Difficulty Level:
Medium
Standard Electrode Potentials
Accuracy: 67%
Total Attempted104
Total Correct70
Total Incorrect34
Difficulty Level:
Medium

Learning Objectives

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Learning Objectives

  • Describe an electrochemical cell and differentiate between galvanic and electrolytic cells.
  • Apply the Nernst equation for calculating the emf of a galvanic cell and define the standard potential of the cell.
  • Derive the relation between standard potential of the cell, Gibbs energy of cell reaction, and its equilibrium constant.
  • Define resistivity (ρ), conductivity (κ), and molar conductivity (Λ) of ionic solutions.
  • Differentiate between ionic (electrolytic) and electronic conductivity.
  • Describe the method for measurement of conductivity of electrolytic solutions and calculation of their molar conductivity.
  • Justify the variation of conductivity and molar conductivity of solutions with change in their concentration.
  • Define 1°m (molar conductivity at zero concentration or infinite dilution).
  • Enunciate Kohlrausch's law and learn its applications.
  • Understand quantitative aspects of electrolysis.
  • Describe the construction of some primary and secondary batteries and fuel cells.
  • Explain corrosion as an electrochemical process.

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Revision Notes & Summary

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Electrochemistry Notes

Objectives

  • Describe an electrochemical cell and differentiate between galvanic and electrolytic cells.
  • Apply Nernst equation for calculating the emf of galvanic cells and define standard potential of the cell.
  • Derive relation between standard potential of the cell, Gibbs energy of cell reaction, and its equilibrium constant.
  • Define resistivity (ρ), conductivity (κ), and molar conductivity (Λ) of ionic solutions.
  • Differentiate between ionic (electrolytic) and electronic conductivity.
  • Describe the method for measurement of conductivity of electrolytic solutions and calculation of their molar conductivity.
  • Justify the variation of conductivity and molar conductivity of solutions with change in their concentration.
  • Define 1°m (molar conductivity at zero concentration or infinite dilution).
  • Enunciate Kohlrausch law and learn its applications.
  • Understand quantitative aspects of electrolysis.
  • Describe the construction of some primary and secondary batteries and fuel cells.
  • Explain corrosion as an electrochemical process.

Key Concepts

Electrochemical Cells

  • Galvanic Cell: Converts chemical energy into electrical energy.
  • Electrolytic Cell: Uses electrical energy to drive a non-spontaneous chemical reaction.

Conductivity and Molar Conductivity

  • Conductivity (κ): Measured in S m⁻¹; depends on the concentration of the electrolyte, nature of solvent, and temperature.
  • Molar Conductivity (Λ): Defined as Λ = κ/c, where c is the concentration.
    • Increases with dilution for weak electrolytes.
    • Decreases with dilution for strong electrolytes.

Faraday's Laws of Electrolysis

  1. First Law: The amount of chemical reaction at an electrode is proportional to the quantity of electricity passed.
  2. Second Law: The amounts of different substances liberated by the same quantity of electricity are proportional to their chemical equivalent weights.

Important Formulas

FormulaDescription
R = ρ(l/A)Resistance in terms of resistivity, length, and area of cross-section.
κ = 1/ρConductivity is the inverse of resistivity.
Λ = κ/cMolar conductivity defined in relation to conductivity and concentration.
E°cell = E°cathode - E°anodeStandard potential of the cell.
ΔG° = -nFE°Gibbs energy related to cell potential.

Examples

  • Example 2.7: Calculate Aₘ for CaCl₂ and MgSO₄ using Kohlrausch's law.
  • Example 2.8: Calculate A° for HAc using known molar conductivities.

Applications

  • Batteries and Fuel Cells: Convert chemical energy into electrical energy; used in various devices.
  • Corrosion: An electrochemical phenomenon affecting metals.
  • Hydrogen Economy: Hydrogen as a renewable energy source through electrochemical processes.

Summary

Electrochemistry involves the study of chemical reactions that produce electrical energy and the use of electrical energy to drive chemical reactions. Key concepts include the types of electrochemical cells, conductivity, molar conductivity, and Faraday's laws of electrolysis.
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Practice Test – MCQs, True/False

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Multiple Choice Questions

A.

0.00 V

B.

1.00 V

C.

-0.76 V

D.

2.87 V
Correct Answer: A

Solution:

The standard electrode potential of the hydrogen electrode is assigned as 0.00 V.

Chapter Concept:

Standard Electrode Potentials

A.

It converts electrical energy into chemical energy.

B.

It converts chemical energy directly into electrical energy.

C.

It stores electrical energy for later use.

D.

It uses mechanical energy to generate electrical energy.
Correct Answer: B

Solution:

A fuel cell directly converts the chemical energy of a fuel into electrical energy, making it highly efficient.

Chapter Concept:

Electrochemical Cells

A.

The cell continues to function as a galvanic cell.

B.

The cell stops functioning.

C.

The cell starts functioning as an electrolytic cell.

D.

The cell explodes.
Correct Answer: C

Solution:

When the external voltage exceeds the cell potential, the galvanic cell starts functioning as an electrolytic cell, driving the reaction in the opposite direction.

Chapter Concept:

Electrochemical Cells

A.

21600 C

B.

7200 C

C.

18000 C

D.

3600 C
Correct Answer: A

Solution:

Charge, Q=It=2×3×3600=21600Q = It = 2 \times 3 \times 3600 = 21600 C.

Chapter Concept:

Faraday's Laws of Electrolysis

A.

The type of electrolyte used.

B.

The distance between electrodes and their area of cross-section.

C.

The temperature of the solution.

D.

The concentration of the electrolyte.
Correct Answer: B

Solution:

The cell constant G∗G^* depends on the distance between the electrodes and their area of cross-section.

Chapter Concept:

Conductivity and Molar Conductivity

A.

Zinc

B.

Silver

C.

Gold

D.

Platinum
Correct Answer: A

Solution:

Zinc can displace copper from a solution of copper sulfate because zinc is more reactive than copper, as indicated by its more negative standard electrode potential.

Chapter Concept:

Standard Electrode Potentials

A.

It can be recharged multiple times.

B.

The chemical reaction occurs only once and cannot be reused.

C.

It uses a lead anode and a lead dioxide cathode.

D.

It is used in devices like automobiles and inverters.
Correct Answer: B

Solution:

Primary batteries, such as the dry cell, undergo a chemical reaction only once and cannot be recharged.

Chapter Concept:

Primary and Secondary Batteries

A.

Using the degree of dissociation and molar conductivity.

B.

By measuring the conductivity of a strong electrolyte.

C.

By calculating the difference in conductivities of two strong electrolytes.

D.

By using the standard electrode potential.
Correct Answer: A

Solution:

Kohlrausch's Law helps in determining the dissociation constant of a weak electrolyte by using the degree of dissociation α=ΛmΛm∘\alpha = \frac{\Lambda_m}{\Lambda^\circ_m} and the relation Ka=cα21−αK_a = \frac{c\alpha^2}{1-\alpha}.

Chapter Concept:

Kohlrausch's Law

A.

0.1233

B.

0.2313

C.

0.3123

D.

0.2133
Correct Answer: A

Solution:

The degree of dissociation α\alpha is calculated as α=ΛmΛm0=48.15390.5=0.1233\alpha = \frac{\Lambda_m}{\Lambda^0_m} = \frac{48.15}{390.5} = 0.1233.

Chapter Concept:

Degree of Dissociation and Dissociation Constant from Conductance

A.

Because weak electrolytes dissociate completely at high concentrations.

B.

Because weak electrolytes show steep increase in molar conductivity on dilution.

C.

Because weak electrolytes have constant molar conductivity.

D.

Because weak electrolytes do not dissociate at all.
Correct Answer: B

Solution:

Weak electrolytes show a steep increase in molar conductivity on dilution due to increased dissociation, making simple extrapolation inaccurate.

Chapter Concept:

Variation of Conductivity for Strong and Weak Electrolytes

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True or False

Correct Answer: True

Solution:

The Nernst equation is indeed used to calculate the electrode potential under non-standard conditions. At 298 K, it simplifies to the given form, where QQ is the reaction quotient, nn is the number of moles of electrons transferred, and Ecell∘E^\circ_{cell} is the standard cell potential.

Chapter Concept :

Nernst Equation

Correct Answer: True

Solution:

The standard hydrogen electrode is used as a reference point with an assigned potential of zero, against which all other electrode potentials are measured.

Chapter Concept :

Standard Electrode Potentials

Correct Answer: True

Solution:

Faraday's second law of electrolysis indeed states that the amounts of different substances liberated by the same quantity of electricity passing through the electrolytic solution are proportional to their chemical equivalent weights.

Chapter Concept :

Faraday's Laws of Electrolysis

Correct Answer: True

Solution:

Faraday's first law states that the amount of chemical reaction at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.

Chapter Concept :

Faraday's Laws of Electrolysis

Correct Answer: True

Solution:

According to the standard convention for representing galvanic cells, the anode is placed on the left and the cathode on the right.

Chapter Concept :

Galvanic Cell Representation and Cell Potential

Correct Answer: True

Solution:

In a galvanic cell, oxidation occurs at the anode, which is negatively charged compared to the solution. This is because electrons are released during oxidation, creating a negative charge at the anode.

Chapter Concept :

Electrochemical Cells

Correct Answer: True

Solution:

For weak electrolytes, the degree of dissociation α\alpha is indeed calculated using α=ΛmΛm∘\alpha = \frac{\Lambda_m}{\Lambda^\circ_m}. This formula relates the molar conductivity at a given concentration to the limiting molar conductivity, which is the conductivity at infinite dilution.

Chapter Concept :

Degree of Dissociation and Dissociation Constant from Conductance

Correct Answer: True

Solution:

Kohlrausch's law of independent migration of ions states that the limiting molar conductivity of an electrolyte can be represented as the sum of the individual contributions of the anion and cation of the electrolyte.

Chapter Concept :

Kohlrausch's Law

Correct Answer: True

Solution:

The standard electrode potential is indeed measured relative to the standard hydrogen electrode, which is assigned a potential of zero. This serves as a reference point for measuring the reduction potentials of other electrodes.

Chapter Concept :

Standard Electrode Potentials

Correct Answer: False

Solution:

Ionic conductance in solutions increases with an increase in temperature due to the decreased viscosity of the solvent and increased mobility of ions.

Chapter Concept :

Ionic and Electronic Conductance

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