Page |1

RUBY PARK PUBLIC SCHOOL, KOLKATA

CLASS - XII
SUBJECT - CHEMISTRY
CHAPTER - ELECTROCHEMISTRY

WORKSHEET - II

Electrochemical Cells
1. Consider the following figure and answer the following questions.

(i) Cell ‘A’ has Ecell = 2V and cell ‘B’ has Ecell = 1.1V which of the two cells ‘A’ or ‘B’ will
act as an electrolytic cell. Which electrode reactions will occur in this cell?
(ii) If cell ‘A’ has Ecell = 0.5V and cell ‘B’ has Ecell = 1.1V then what will be the reactions at
anode and cathode?
2. A galvanic cell has electrical potential of 1.1V. If an opposing potential of 1.1V is applied
to this cell, what will happen to the cell reaction and current flowing through the cell?
3. Consider the following figure and answer the following questions.

(i) Write the direction of electron flow?

(ii) Is silver plate the anode or cathode?
(iii) What will happen if salt bridge is removed?
(iv) When will the cell stop functioning?
(v) How will concentration of Zn2+ ions and Ag+ ions be affected when the cell functions?
1 (vi) How will the concentration of Zn2+ ions and Ag+ ions be affected after the cell becomes
‘dead’?
4. Depict the galvanic cell in which the cell reaction is Cu + 2Ag+ → 2Ag + Cu2+
5. Why does a galvanic cell become dead after some time?
6. Why is alternating current used for measuring resistance of an electrolytic solution?

DR. ABHISHEK PAL | RUBY PARK PUBLIC SCHOOL (28-05-2023)

 Page |2

EMF of a Cell
7. Can you store copper sulphate solutions in a zinc pot?
8. Which amongst the following is the strongest oxidising agent?
Cl2 (g) + 2e- 2Cl- ; Eo = 1.36V
- + 2+
MnO4 + 8H + 5e- Mn + 4H2O; Eo = 1.51V
Cr2O72- + 14H+ + 6e- 2Cr3+ + 7H2O; Eo = 1.33V
o
9. Using the E values of A and B, predict which is better for coating the surface of iron
[EoFe2+/Fe = -0.44V] to prevent corrosion and why?
[Given: EoA2+/A = -2.37V, EoB2+/B = -0.14V]
10. Given the standard electrode potentials.
K+/K = –2.93V
Ag+/Ag = 0.80V
Hg2+/Hg = 0.79V
Mg2+/Mg = –2.37 V
Cr3+/Cr = – 0.74V
Arrange these metals in their increasing order of reducing power.
Nernst Equation
11. Calculate Eocell for the following reaction at 298K:
2Al(s) + 3Cu2+ (0.01M) 2Al3+ (0.01M) + 3Cu(s)
Given: Ecell = 1.98 V
12. Represent the cell in which the following reaction takes place:
2Al(s) + 3Ni2+ (0.1M) 2Al3+ (0.01M) + 3Ni(s)
o
Calculate the emf if E cell = 1.41V.
13. Calculate the standard reduction potential of Ni2+/Ni electrode when the cell potential for
the cell Ni/Ni2+ (1M) // Cu2+ (1M)/Cu is 0.59 V.
(E°Cu2+/Cu = 0.34 V).
14. Calculate the potential for half-cell containing 0.10M K2Cr2O7 (aq), 0.20M Cr3+ (aq) and
1.0×10-4M H+ (aq). The half cell reaction is:
Cr2O72- (aq) + 14H+ (aq) + 6e- 2Cr3+ (aq) + 7H2O (l); and the standard electrode
o
potential is given as E = 1.33V.
15. Calculate emf and ΔG for the following cell at 298K:
Mg (s) / Mg2+ (0.01M) // Ag+ (0.0001M) / Ag (s)
Given: EoMg2+/Mg = - 2.37V, EoAg+/Ag = + 0.80V
16. Estimate the minimum potential difference needed to reduce Al2O3 at 500oC. The free
energy change for the decomposition reaction
2/3 Al2O3 4/3 Al + O2 is 960 kJ (F = 96,500 C mol-1)
17. Calculate ΔGo and logKc for the following reaction at 298K:
Zn (s) + Cd2+ (aq) Zn2+ (aq) + Cd (s)
[Given: E Cd2+/Cd = - 0.403 V, EoZn2+/Zn = - 0.763 V]
o

18. Calculate ΔGo and logKc for the following reaction at 298K:
2Cr (s) + 3Fe2+ (aq) 2Cr3+ (aq) + 3Fe (s) [Given: Eocell = 0.30 V]
19. The emf of a cell corresponding to the reaction
Zn (s) + 2H+ (aq) Zn2+ (0.1M) + H2 (g, 1atm) is 0.28 volt at 25oC.
Write the half-cell reactions and calculate the pH of the solution at the hydrogen electrode.
2 [EoZn2+/Zn = - 0.76 V, EoH+/H2 = 0 V]
20. At what pH of HCl solution will hydrogen gas electrode show electrode potential of
- 0.118V? H2 gas is passed at 298K and 1 atm pressure.
21. Calculate the potential of hydrogen electrode in contact with a solution whose pH is 10.

DR. ABHISHEK PAL | RUBY PARK PUBLIC SCHOOL (28-05-2023)

 Page |3

Conductance in Electrolytic Solutions

22. Define the term: Limiting molar conductivity
23. Why does the conductivity of a solution decrease with dilution?
24. Solutions of two electrolytes ‘A’ and ‘B’ are diluted. The m Λ of ‘B’ increases 1.5 times
while that of A increases 25 times. Which of the two is a strong electrolyte? Justify your
answer.
25. Why on dilution the Λm of CH3COOH increases drastically, while that of CH3COONa
increases gradually?
26. (i) How does molar conductivity vary with increase in concentration for strong electrolyte
and weak electrolyte?
(ii) How can you obtain limiting molar conductivity (Ʌom) for weak electrolyte?
27. The electrical resistance of a column of 0.05 M NaOH solution of diameter 1 cm and length
50 cm is 5.55 × 103 Ω. Calculate its resistivity, conductivity and molar conductivity.
28. The molar conductivity of a 1.5M solution of an electrolyte is found to be 138.9 Scm2 mol-1
Calculate the conductivity of this solution.
29. The conductivity of 0.20 M solution of KCl at 298K is 0.025 S cm-1. Calculate its molar
conductivity.
30. Resistance of a conductivity cell filled with 0.1 molL-1 KCl solution is 100 Ω. If the
resistance of the same cell when filled with 0.02 molL-1 KCl solution is 520Ὡ, calculate the
conductivity and molar conductivity of 0.02 molL-1 KCl solution. The conductivity of 0.1
molL-1 KCl solution is 1.29×10-2 Ω -1cm-1.
Kohlrausch’s Law
31. (i) State Kohlrausch law of independent migration of ions.
(ii) Suggest a way to determine the Λom value of water.
32. Calculate Ʌom for acetic acid.
Given that Ʌom (HCl) = 426 S cm2 mol-1, Ʌom (NaCl) = 126 S cm2 mol-1, Ʌom (CH3COONa)
= 91 S cm2 mol-1
33. From the following molar conductivities at infinite dilution, calculate Ʌom for NH4OH.
Ʌom for Ba(OH)2 = 457.6 Ω-1 cm2 mol-1
Ʌom for BaCl2 = 240.6 Ω-1 cm2 mol-1
Ʌom for NH4Cl = 129.8 Ω-1 cm2 mol-1
34. At 291K, the molar conductivities at infinite at dilution of NH4Cl, NaOH and NaCl are
129.8, 217.4 and 108.9 S cm2 mol-1 respectively. If the molar conductivity of a continormal
solution of NH4OH is 9.33 S cm2 mol-1, what is the percentage dissociation of NH4OH at
this dilution? Also calculate the dissociation constant of NH4OH.
35. Conductivity of 2.5×10-4 (M) methanoic acid is 5.25×10-5 S cm-1. Calculate its molar
conductivity and degree of dissociation.
[Given: λo(H+) = 349.5 S cm2 mol-1 and λo(HCOO-) = 50.5 S cm2 mol-1]
36. Calculate the degree of dissociation (α) of acetic acid if its molar conductivity (Ʌm) is 39.05
S cm2 mol-1.
[Given: λo(H+) = 349.6 S cm2 mol-1 and λo(CH3COO-) = 40.9 S cm2 mol-1]
Faraday’s Law and Electrolysis
37. Value of standard electrode potential for the oxidation of Cl- ions is more positive than that
3 of water, even then in the electrolysis of aqueous sodium chloride, why is Cl- oxidised at
anode instead of water?
38. When acidulated water (dil.H2SO4 solution) is electrolysed, will the pH of the solution be
affected? Justify your answer.
39. How will the pH of brine (aq. NaCl solution) be affected when it is electrolysed?

DR. ABHISHEK PAL | RUBY PARK PUBLIC SCHOOL (28-05-2023)

 Page |4

40. Predict the products of electrolysis in each of the following:

(i) An aqueous solution of AgNO3 with silver electrodes.
(ii) An aqueous solution of AgNO3 with platinum electrodes.
(iii) A dilute solution of H2SO4 with platinum electrodes.
(iv) An aqueous solution of CuCl2 with platinum electrodes.
41. How much charge is required for the following reductions:
(i) 1 mol of Al3+ to Al?
(ii) 1 mol of Cu2+ to Cu?
(iii) 1 mol of MnO4– to Mn2+?
42. How much electricity in terms of Faraday is required to produce
(i) 20.0 g of Ca from molten CaCl2?
(ii) 40.0 g of Al from molten Al2O3?
43. (i) A current of 1.50 A was passed through an electrolytic cell containing AgNO3 solution
with inert electrodes. The weight of Ag deposited was 1.50 g. How long did the current
flow?
(ii) Write the reactions taking place at the anode and cathode in the above cell.
(iii) Give reactions taking place at the two electrodes if these are made up of Ag.
44. If a current of 0.5 ampere flows through a metallic wire for 2 hours, then how many
electrons would flow through the wire?
45. A solution of Ni(NO3)2 is electrolysed between platinum electrodes using a current of 5
amperes for 20 minutes. What mass of Ni is deposited at the cathode?
46. Aqueous copper sulphate solution and aqueous silver nitrate solution are electrolysed by 1A
current for 10 minutes in separate electrolytic cells. Will the mass of copper and silver
deposited on the cathode be same or different? Explain your answer.
47. Calculate the time to deposit 1.27 g of copper at cathode when a current of 2A was passed
through the solution of CuSO4.
(Molar mass of Cu = 63.5 g mol-1, 1F = 96,500 C mol-1)
48. When a current of 0.75 A is passed through a CuSO4 solution for 25 min, 0.369 g of copper
is deposited at the cathode. Calculate the atomic mass of copper.
49. How many moles of mercury will be produced by electrolysing 1.0M Hg(NO3)2 solution
with a current of 2A for 3 hours?
50. How many molecules of chlorine should be deposited from molten sodium chloride in one
minute by a current of 300 milliampere?
51. Silver is electro-deposited on a metallic vessel of total surface area 500 cm2 by passing a
current of 0.5 amp for two hours. Calculate the thickness of silver deposited.
[Given: Density of silver = 10.5 g cm-3, Atomic mass of silver = 108 amu, F = 96500 C
mol-1]
Lead accumulator, Fuel cells and Corrosion
52. (i) Define the term: Fuel cell
(ii) State two advantages of H2-O2 fuel cell over ordinary cell.
53. The chemistry of corrosion of iron is essentially an electrochemical phenomenon. Explain
the reactions occurring during the corrosion of iron in the atmosphere.
54. Unlike dry cell, the mercury cell has a constant cell potential throughout its useful life.
Why?
55. (i) What type of a battery is lead storage battery?
4 (ii) Write the anode and cathode reactions and the overall cell reaction occurring in the
operation of a lead storage battery.
56. For the given cells:
Lead storage cell, Mercury cell, Fuel cell and Dry cell

DR. ABHISHEK PAL | RUBY PARK PUBLIC SCHOOL (28-05-2023)

 Page |5

Answer the following:

(i) Which cell is used in hearing aids?
(ii) Which cell was used in Apollo space programme?
(iii) Which cell is used in automobiles and inverters?
(iv) Which cell does not have long life?
57. Write the cell reaction of a lead storage battery when it is discharged. How does the density
of the electrolyte change when the battery is discharged?

DR. ABHISHEK PAL | RUBY PARK PUBLIC SCHOOL (28-05-2023)