[100] Electrochemistry exam questions and solutions (pdf)

Electrochemistry Exam Questions and Solutions – Overview

Electrochemistry is the branch of chemistry that studies the relationship between chemical reactions and electrical energy. It primarily deals with oxidation-reduction (redox) reactions, where electrons are transferred between species. These reactions occur in electrochemical cells, which are of two main types: galvanic (voltaic) cells that generate electricity from spontaneous reactions, and electrolytic cells that use electrical energy to drive non-spontaneous reactions. Key concepts include electrode potentials, standard reduction potentials, and the electrochemical series, which helps predict the feasibility of redox reactions.

Another important aspect of electrochemistry is the Nernst equation, which relates the electrode potential to the concentration of reactants and products. This allows us to calculate cell potentials under non-standard conditions. Additionally, electrochemistry plays a crucial role in understanding batteries, corrosion, electroplating, and fuel cells. Concepts like Faraday’s laws of electrolysis help quantify the amount of substance deposited or liberated during electrolysis based on the charge passed.

Electrochemistry is widely applied in industries and daily life. It is essential in designing energy storage systems like lithium-ion batteries, preventing corrosion of metals, and in analytical techniques such as potentiometry. Mastery of numerical problem-solving in electrochemistry is vital for exams, as it involves applying formulas related to EMF, Gibbs free energy, equilibrium constants, and electrolysis calculations.

100 Practice Numerical Problems with Answers

Section A: Basic Concepts (1–20)

1. Calculate EMF if E°cell = 1.10 V → Answer: 1.10 V
2. Convert 2 Faraday into charge → Answer: 193000 C
3. Charge required for 1 mole electrons → Answer: 96500 C
4. EMF when cathode = 0.34 V, anode = –0.76 V → Answer: 1.10 V
5. ΔG° for n=2, E°=1.1 V → Answer: –212.3 kJ
6. Oxidation number change in Zn → Answer: +2
7. Faradays for 2 mol electrons → Answer: 2 F
8. Voltage of Daniell cell → Answer: 1.10 V
9. Standard hydrogen electrode potential → Answer: 0 V
10. Cell potential if both electrodes equal → Answer: 0 V
11. Unit of EMF → Answer: Volt
12. Charge of 0.5 mol electrons → Answer: 48250 C
13. n-factor of Cu²⁺ → Cu → Answer: 2
14. Number of electrons in Fe³⁺ → Fe²⁺ → Answer: 1
15. Faraday constant → Answer: 96500 C/mol
16. Cathode reaction in Daniell cell → Answer: Cu²⁺ + 2e⁻ → Cu
17. Anode reaction → Answer: Zn → Zn²⁺ + 2e⁻
18. Sign of ΔG for spontaneous → Answer: Negative
19. Relation ΔG and E → Answer: ΔG = –nFE
20. Units of ΔG → Answer: Joules

Section B: Nernst Equation (21–40)

21. EMF at 298K, n=1, Q=10 → Answer: E = E° – 0.059
22. Log(1) → Answer: 0
23. If Q=1, E= → Answer: E°
24. EMF when Q=100 → Answer: E° – 0.118 V
25. If E°=1V, Q=10 → Answer: 0.941 V
26. Temperature constant (298K) → Answer: 0.0591
27. If n=2, constant → Answer: 0.0295
28. EMF decreases when Q → Answer: Increases
29. Equilibrium EMF → Answer: 0
30. If Q=K → Answer: E=0
31. log10 = → Answer: 1
32. log100 = → Answer: 2
33. Effect of concentration increase → Answer: EMF changes
34. Nernst equation unit → Answer: Volt
35. E when Q very small → Answer: High
36. E when Q large → Answer: Low
37. n increases → effect → Answer: Smaller change
38. Temperature increases → Answer: EMF changes
39. Standard condition temp → Answer: 298K
40. Gas constant value → Answer: 8.314 J/mol·K

Section C: Electrolysis (41–70)

41. Charge for 1 mol Ag deposition → Answer: 96500 C
42. Ag⁺ + e⁻ → Ag, n= → Answer: 1
43. Cu²⁺ needs electrons → Answer: 2
44. Mass deposited formula → Answer: m = ZIt
45. Z unit → Answer: g/C
46. Current unit → Answer: Ampere
47. 1 A for 1 sec → charge → Answer: 1 C
48. 2 A for 10 s → Answer: 20 C
49. 96500 C deposits Ag → Answer: 108 g
50. 48250 C deposits Ag → Answer: 54 g
51. Equivalent weight of Cu → Answer: 31.75
52. m ∝ Q → Answer: True
53. m ∝ I → Answer: True
54. m ∝ t → Answer: True
55. Faraday law number → Answer: 2
56. Electrolysis is → Answer: Non-spontaneous
57. Cathode reaction → Answer: Reduction
58. Anode reaction → Answer: Oxidation
59. Gas evolved depends on → Answer: Electrolyte
60. H₂ formed requires → Answer: 2 electrons
61. O₂ formation electrons → Answer: 4
62. Charge for O₂ (1 mol) → Answer: 386000 C
63. 1F deposits → Answer: 1 equivalent
64. Electroplating uses → Answer: Electrolysis
65. Unit of Z → Answer: g/C
66. Efficiency formula → Answer: Actual/Theoretical ×100
67. Current density unit → Answer: A/m²
68. Time unit → Answer: sec
69. Coulomb definition → Answer: Charge unit
70. Electrolyte conducts via → Answer: Ions

Section D: Advanced Numericals (71–100)

71. ΔG = –nFE, n=1, E=1 → Answer: –96500 J
72. ΔG for n=2, E=1.5 → Answer: –289500 J
73. K from E°=1 → Answer: ~10¹⁷
74. logK relation → Answer: nE°/0.059
75. If E°=0 → Answer: K=1
76. E° positive → Answer: K>1
77. E° negative → Answer: K<1
78. Corrosion is → Answer: Electrochemical
79. Rusting involves → Answer: Fe oxidation
80. Fuel cell converts → Answer: Chemical to electrical
81. Battery stores → Answer: Electrical energy
82. Lead-acid battery voltage → Answer: 2 V
83. Dry cell voltage → Answer: 1.5 V
84. Lithium battery voltage → Answer: ~3.7 V
85. EMF unit → Answer: Volt
86. Internal resistance unit → Answer: Ohm
87. Ohm’s law → Answer: V=IR
88. Conductivity unit → Answer: S/m
89. Resistivity unit → Answer: Ω·m
90. Specific conductance symbol → Answer: κ
91. Molar conductance unit → Answer: S·cm²/mol
92. Kohlrausch law applies → Answer: Strong electrolytes
93. Degree of dissociation → Answer: α
94. Weak electrolyte α increases with → Answer: Dilution
95. Conductance increases with → Answer: Temperature
96. Ionic mobility unit → Answer: cm²/V·s
97. Transference number sum → Answer: 1
98. Cathode gain mass → Answer: Positive
99. Anode loses mass → Answer: True
100. EMF independent of → Answer: Size of electrodes