Electrochemistry — 50 MCQs

1. Oxidation is:

1. Gain of electrons
2. Loss of electrons ✅
3. Gain of protons
4. Gain of mass

2. Standard electrode potential of SHE is defined as:

1. +1.00 V
2. 0.00 V ✅
3. -0.76 V
4. Depends on concentration

3. Cell notation anode | anode solution || cathode solution | cathode. Which side undergoes oxidation?

1. Cathode
2. Anode ✅
3. Both
4. Neither

4. E°cell = +0.34 V. The cell reaction is:

1. Non-spontaneous as written
2. Spontaneous as written ✅
3. At equilibrium
4. Impossible

5. ΔG° and E°cell are related by:

1. ΔG° = nFE°cell
2. ΔG° = -nFE°cell ✅
3. ΔG° = -RT ln K only
4. No relation

6. Nernst equation allows calculation of:

1. Standard potentials only
2. Cell potential under non-standard conditions ✅
3. Only ΔG°
4. Only ionic strength

7. Faraday's constant (F) is approximately:

1. 8.314 J mol⁻¹ K⁻¹
2. 96485 C mol⁻¹ ✅
3. 1.602×10^-19 C
4. 0.05916 V

8. In electrolysis, the mass of substance deposited at an electrode is proportional to:

1. Voltage only
2. Total charge passed (Q = It) ✅
3. Time only
4. Resistance only

9. In a Daniell cell (Zn|Zn2+||Cu2+|Cu), which electrode is the cathode?

1. Zn
2. Cu ✅
3. Salt bridge
4. Both are cathodes

10. Which device converts chemical energy into electrical energy?

1. Electrolytic cell
2. Galvanic (voltaic) cell ✅
3. Both always
4. Neither

11. Which of the following increases cell potential for concentration cells?

1. Making concentrations equal
2. Increasing concentration difference ✅
3. Adding catalyst
4. Adding inert gas

12. Corrosion of iron is an example of:

1. Purely chemical reaction
2. Electrochemical oxidation ✅
3. Photochemical reaction
4. Thermal decomposition

13. Cathodic protection prevents corrosion by:

1. Making the metal the anode
2. Making the metal the cathode (sacrificial anode or impressed current) ✅
3. Increasing oxygen concentration
4. Heating the metal

14. In electroplating, metal is deposited at the:

1. Anode
2. Cathode ✅
3. Salt bridge
4. Both electrodes equally

15. The Nernst equation at 25°C simplifies to E = E° - (0.05916/n) log Q. What does n represent?

1. Number of moles of reactant
2. Number of electrons transferred in the cell reaction ✅
3. Number of species in equation
4. Temperature factor

16. Which metal will displace Ag+ from solution: Cu, Zn, or Au?

1. Au
2. Zn (more easily oxidized) ✅
3. Cu
4. None

17. Which statement about catalysts in electrochemical cells is TRUE?

1. Catalyst changes E°cell
2. Catalyst increases rate towards equilibrium but does not change E°cell ✅
3. Catalyst changes number of electrons transferred
4. Catalyst prevents electron transfer

18. In electrolysis of molten NaCl, which is produced at cathode?

1. Cl2 gas
2. Na metal ✅
3. NaCl solid
4. H2 gas

19. A positive E°red indicates that the species is:

1. Strong reducing agent
2. Good oxidizing agent (readily reduced) ✅
3. Neutral always
4. Unreactive

20. Which cell will have E°cell = 0?

1. Any galvanic cell
2. Cell with non-zero Q
3. Concentration cell at equilibrium (identical conditions) ✅
4. Electrolytic cell under current

21. Which of the following increases the emf of a cell at constant temperature?

1. Decrease in concentration difference
2. Increase in concentration difference (per Nernst) ✅
3. Adding catalyst
4. Short-circuiting the cell

22. Which reaction occurs at cathode in an electrochemical cell?

1. Oxidation
2. Reduction ✅
3. No reaction
4. Both oxidation and reduction equally

23. The theoretical amount of substance produced in electrolysis depends on Faraday's laws and is independent of:

1. Total charge passed
2. Equivalent weight of substance
3. Electrode surface area (only affects rate) ✅
4. Time of electrolysis (through Q)

24. Which term describes the flow of ions in an electrolyte solution under applied potential?

1. Convection
2. Ionic conduction ✅
3. Electron conduction only
4. Diffusion only

25. Which battery chemistry is commonly used in portable electronics?

1. Lead-acid
2. Li-ion (Lithium-ion) ✅
3. Zinc-carbon only
4. Mercury battery only

26. During electrolysis of aqueous CuSO4 with inert electrodes, which gas is evolved at anode?

1. Cu vapor
2. O2 (from oxidation of water) ✅
3. H2
4. SO2

27. Which property of electrodes affects overpotential?

1. Electrode material and surface condition ✅
2. Only electrolyte color
3. Only temperature always
4. None of the above

28. In concentration cell made of same electrodes, the emf is generated because of:

1. Different electrode materials
2. Difference in ion concentrations on the two sides ✅
3. Temperature difference only
4. External battery connected

29. Electrochemical series helps predict which of the following?

1. Solubility in water only
2. Spontaneity of redox reactions and displacement reactions ✅
3. Color of ions only
4. pH of solution

30. If ΔG = -120 kJ for a cell reaction at 298 K and n = 2, E°cell is approximately (F = 96485 C mol⁻¹):

1. 0.62 V
2. 0.62 V ✅ (ΔG=-nFE° ⇒ E° = -ΔG/(nF) ≈ 120000/(2×96485)≈0.622 V)
3. -0.62 V
4. 62 V

31. Which statement about electrolytic cells is FALSE?

1. They require external power source
2. They always produce electricity ✅ (false — they consume electricity)
3. They can be used for electroplating
4. They drive non-spontaneous reactions

32. What is the role of a salt bridge in a galvanic cell?

1. Provide electrons
2. Maintain electrical neutrality by ion flow ✅
3. Increase cell voltage dramatically
4. Act as a catalyst

33. Hydrogen fuel cells produce electricity by combining H2 and O2 to form:

1. CO2
2. H2O (water) ✅
3. H2O2 only
4. HCl

34. In electrochemical kinetics, Tafel slope relates current density to:

1. Concentration only
2. Overpotential (η) and reaction rate ✅
3. Temperature only
4. Color of electrode

35. Which factor does NOT change the standard reduction potential of an electrode?

1. Temperature
2. Pressure (for gases)
3. Presence of a catalyst on electrode (does not change E°) ✅
4. Concentration (E not E°)

36. Which is true for primary batteries?

1. They are rechargeable
2. They are non-rechargeable and used once ✅
3. They always use lithium chemistry
4. They operate at very high temperatures only

37. Which ion mobility contributes to conductivity in an aqueous electrolyte?

1. Only cations
2. Both cations and anions ✅
3. Only electrons
4. Only protons

38. Overpotential is required to:

1. Increase theoretical cell voltage
2. Compensate kinetic barriers so reaction proceeds at practical rate ✅
3. Reduce electrode area
4. Change electrolyte composition

39. Which metal is commonly used as sacrificial anode to protect steel structures?

1. Gold
2. Zinc (or magnesium) ✅
3. Silver
4. Lead

40. In a redox titration using a potentiometric method, endpoint is detected by:

1. Color change only
2. Sharp change in measured potential ✅
3. Temperature change only
4. pH reaching 7

41. Which of the following reduces internal resistance of a battery?

1. Longer current path
2. Larger electrode surface area and better electrolyte conductivity ✅
3. Thinner separators only
4. Lower electrolyte concentration

42. Which electrochemical technique measures reaction rates at electrodes?

1. Gravimetry only
2. Electrochemical impedance spectroscopy and voltammetry ✅
3. pH titration only
4. Colorimetry

43. Which of the following is a disadvantage of lead-acid batteries?

1. High energy density compared to Li-ion
2. Heavy and lower cycle life compared to modern batteries ✅
3. They are non-rechargeable
4. They do not produce high currents

44. Which gas evolution may cause pitting corrosion in stainless steel during electrolysis?

1. Hydrogen only
2. Chlorine (from chloride oxidation) ✅
3. Oxygen only
4. Nitrogen only

45. Which parameter directly affects the standard electrode potential value?

1. Concentration under standard conditions (1 M) — standard potentials defined at these conditions ✅
2. Electrode surface area
3. Cell current
4. External circuit resistance

46. Which of the following is used as reference electrode in lab besides SHE?

1. Mercury/mercurous chloride (Calomel) electrode ✅
2. Silver chloride only
3. Platinum hydrogen only
4. None of the above

47. Which concept explains why metals corrode faster in presence of saltwater?

1. Lower oxygen content
2. Higher ionic conductivity increases electrochemical reaction rates ✅
3. Lower pH only
4. Higher temperature always

48. In electrorefining, impure metal is made anode so that:

1. Impurities are plated onto cathode preferentially
2. Impurities either remain in solution or fall as anode mud while pure metal plates at cathode ✅
3. Pure metal dissolves only
4. No metal dissolves

49. Which electrochemical cell has negative E°cell under standard conditions?

1. All concentration cells
2. A galvanic cell whose written reaction is non-spontaneous under standard conditions ✅
3. Hydrogen fuel cell always
4. None of the above