Electrochemistry
Multiple Choice Questions for NEET and IIT-JEE
1. Strong electrolytes are those which:
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Correct Answer: (d)
Strong electrolytes are substances that dissociate or ionize completely into their constituent ions in aqueous solution at practically all concentrations and dilutions.
2. Electrolytes when dissolved in water dissociates into ions because:
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Correct Answer: (d)
Water has a high dielectric constant (approx. 80), which greatly reduces the electrostatic forces of attraction holding the oppositely charged ions together in an ionic crystal lattice, leading to dissociation.
3. Which one of the following metals could not be obtained on electrolysis of aqueous solution of its salts?
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Correct Answer: (a)
Magnesium (Mg) has a very high negative reduction potential compared to water. In an aqueous solution, water is preferentially reduced at the cathode to yield hydrogen gas rather than Mg metal. Mg can only be obtained by the electrolysis of its fused (molten) salts.
4. Electrolysis involves oxidation and reduction respectively at:
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Correct Answer: (a)
By rule, oxidation always takes place at the anode (loss of electrons) and reduction always takes place at the cathode (gain of electrons) in any electrochemical or electrolytic cell.
5. Which of the following compound will not undergo decomposition on passing electricity through aqueous solution?
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Correct Answer: (a)
Sugar (sucrose) is a covalent molecular compound that does not ionize or dissociate into ions in water. Because there are no free charge carriers, its solution does not conduct electricity and won't undergo electrolytic decomposition.
6. When the sample of copper with zinc impurity is to be purified by electrolysis, the appropriate electrodes are:
| Cathode | Anode |
|---|---|
| (a) pure zinc | pure copper |
| (b) impure sample | pure copper |
| (c) impure zinc | impure sample |
| (d) pure copper | impure sample |
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Correct Answer: (d)
In electrolytic refining of copper, the impure copper metal sample is made the anode (where it dissolves), and a thin sheet of pure copper is made the cathode (where pure copper ions deposit). Zinc, being more electropositive, remains in the electrolyte solution as Zn2+ ions and does not deposit at the cathode under these operating conditions.
7. In the electrolytic cell, flow of electrons is from:
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Correct Answer: (d)
Note: The options provided in the prompt contain minor typographical mismatches. The correct path is anode to cathode through the external circuit. Electrons leave the anode (where oxidation occurs) and travel through the external power supply wire to reach the cathode (where reduction occurs).
8. The electric conduction of a salt solution in water depends on the:
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Correct Answer: (d)
Electrical conduction in solution relies on the presence of free moving ions. The higher the extent of ionization (fraction of molecules converted into ions), the greater the number of charge carriers available to conduct electricity.
9. During the electrolysis of fused NaCl, which reaction occurs at anode?
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Correct Answer: (a)
At the anode, negative anions (Cl-) discharge by losing electrons (oxidation): 2Cl- → Cl2(g) + 2e-.
10. Pure water does not conduct electricity because it:
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Correct Answer: (c)
Pure water is a very weak electrolyte and undergoes self-ionization to an extremely small extent ([H+] = [OH-] = 10-7 mol/L). Due to this lack of significant free ions, it behaves as a poor electrical conductor.
11. Use of electrolysis is:
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Correct Answer: (c)
Electrolysis is used commercially both for purifying metals (electrorefining) and for depositing a layer of one metal onto another decorative or protective metal object (electroplating).
12. Degree of ionization of a solution depends upon:
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Correct Answer: (d) [Correcting 'none' to 'all']
The degree of ionization depends on several factors: temperature (ionization typically increases with temperature), nature of the solvent (higher dielectric constant increases ionization), and the nature of the electrolyte (strong vs. weak).
13. During electrolysis, the species discharged at cathode are:
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Correct Answer: (b)
Positively charged ions (cations) are attracted to the negatively charged electrode, which is the cathode, where they gain electrons and get discharged.
14. Which of the following liberate hydrogen on reaction with dilute H2SO4?
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Correct Answer: (a) and (b)
Metals positioned above hydrogen in the electrochemical reactivity series can reduce H+ ions from dilute acids to evolve H2 gas. Both Aluminum (Al) and Iron (Fe) are active metals that react with dilute H2SO4. Copper (Cu) and Mercury (Hg) lie below hydrogen and will not react.
15. Amount of electricity that can deposit 108 g of silver from AgNO3 solution is:
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Correct Answer: (a)
The cathode reduction reaction is: Ag+ + e- → Ag. 1 mole of electrons (1 Faraday of electricity) deposits 1 mole of Ag, which corresponds exactly to its molar mass, 108 g.
16. When 9.65 coulomb of electricity is passed through a solution of silver nitrate (atomic weight of Ag = 108) the amount of silver deposited is:
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Correct Answer: (b)
96500 Coulombs (1 F) deposits 108 g of Ag.Therefore, 9.65 C will deposit:
Weight = (108 / 96500) × 9.65 = 0.0108 g = 10.8 mg.
17. Three faradays electricity was passed through an aqueous solution of iron (II) bromide. The weight of iron metal (at. wt. 56) deposited at the cathode (in gram) is:
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Correct Answer: (b)
In FeBr2, iron is present as Fe2+. The reaction is: Fe2+ + 2e- → Fe.
Thus, 2 Faradays deposit 1 mole of Fe (56 g).
3 Faradays will deposit: (56 / 2) × 3 = 84 g.
18. On passing 0.1 faraday of electricity through aluminium metal deposited on cathode is (Al = 27):
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Correct Answer: (c)
Aluminium ion reduction requires 3 electrons: Al3+ + 3e- → Al. 3 Faradays deposit 1 mole of Al (27 g).
0.1 Faraday will deposit: (27 / 3) × 0.1 = 0.9 g.
19. 5 A is passed through a solution of zinc sulphate for 40 min. Find the amount of zinc deposited at the cathode. (At. wt. of Zn ≈ 65.4 g/mol)
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Correct Answer: (a)
Given: Current (I) = 5 A, Time (t) = 40 × 60 = 2400 s. Total Charge Q = I × t = 5 × 2400 = 12000 C.
Zinc is Zn2+, so its valency (n) = 2. Equivalent weight of Zn = 65.4 / 2 = 32.7 g.
Mass (W) = (Equivalent weight × Q) / 96500 = (32.7 × 12000) / 96500 = 4.066 g.
20. On passing 3 A of electricity for 50 min. 1.8 g metal deposits. The equivalent mass of metal is:
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Correct Answer: (b)
Charge passed Q = I × t = 3 × (50 × 60) = 9000 C. According to Faraday's law: Mass = (Eq. Mass × Q) / 96500
1.8 = (Eq. Mass × 9000) / 96500
Eq. Mass = (1.8 × 96500) / 9000 = 19.3.
21. The desired amount of charge for obtaining one mole of Al from Al3+ is:
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Correct Answer: (c)
The reduction reaction is: Al3+ + 3e- → Al. To obtain 1 mole of Al, 3 moles of electrons are required, which equals 3 Faradays or 3 × 96500 C.
22. Electrolysis rules of Faraday's states that mass deposited on electrode is proportional to:
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Correct Answer: (a)
Faraday's First Law of Electrolysis states that the mass (m) of any substance deposited or liberated at an electrode is directly proportional to the quantity of electricity (Q) passed through the electrolyte.
23. During the electrolysis of a solution of AgNO3, 9650 coulombs of charge pass through the electroplating bath, the mass of silver deposited in the cathode will be:
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Correct Answer: (b)
96500 C deposits 1 mole of Ag = 108 g.Therefore, 9650 C (which is exactly one-tenth of 96500 C) will deposit 10.8 g of silver.
24. The number of Faraday's needed to reduce 4 g-equivalents of Cu2+ to Cu metal will be:
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Correct Answer: (c)
By definition, 1 Faraday of electrical charge discharges exactly 1 gram-equivalent of any substance. Therefore, to reduce 4 gram-equivalents of Cu2+, exactly 4 Faradays of electricity are required.
25. In a galvanic cell, the electron flow from:
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Correct Answer: (a)
In a galvanic cell, oxidation takes place at the anode, releasing electrons. These electrons then travel from the anode to the cathode via the external conducting wire circuit.
26. The number of coulombs required to reduce 12.3 g of nitrobenzene to aniline:
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Correct Answer: (d)
The reduction reaction is: C6H5NO2 + 6H+ + 6e- → C6H5NH2 + 2H2O. Molar mass of nitrobenzene (C6H5NO2) = 123 g/mol.
Moles of nitrobenzene given = 12.3 g / 123 g/mol = 0.1 mol.
Since 1 mole requires 6 F, 0.1 mole requires 0.6 F of charge.
Total Charge = 0.6 × 96500 C = 57900 C.
27. During the process of electrolytic refining of copper, some metals present as impurity settle as 'anode mud', these are:
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Correct Answer: (a)
Less electropositive metals (noble metals like Gold (Au), Silver (Ag), and Platinum) present in crude copper do not undergo oxidation at the operating potential. Instead, they drop down intact from the melting anode and settle below it as valuable 'anode mud'.
28. The factor which is not affecting the conductivity of any solution is:
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Correct Answer: (d)
Conductivity of an electrolytic solution is explicitly affected by temperature, dilution (concentration change), and the specific nature of the electrolyte. Hence, all listed options affect it, making "none of these" the right choice.
29. The conductivity of strong electrolyte is:
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Correct Answer: (b)
Note: The question refers to specific conductivity (κ). Specific conductivity decreases with dilution because the number of current-carrying ions per unit volume (cm3) of the solution decreases when solvent is added.
30. Conductivity (unit Siemen) is directly proportional to area of the vessel and the concentration of the solution in it and is inversely proportional to the length of the vessel then the unit of the constant of proportionality is:
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Correct Answer: (c)
Given expression: G = K × (A × C) / l Rearranging for the constant (K): K = (G × l) / (A × C)
Substituting units (SI standard): [S × m] / [m2 × (mol × m-3)] = S m2 mol-1.
31. The unit of equivalent conductivity is:
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Correct Answer: (b) [Adjusting option layout for correct units]
Equivalent conductivity (Λeq) is expressed as κ × 1000 / N. Its functional unit is Ω-1 cm2 eq-1 (or S cm2 eq-1).
32. The electrolytic conductance is a direct measure of:
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Correct Answer: (c)
For weak electrolytes, conductance directly correlates with degree of dissociation because greater dissociation provides more free ions to carry charge.
33. Conductivity of a strong electrolyte:
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Correct Answer: (a)
As dilution increases, the absolute number of ions per unit volume decreases, resulting in a reduction in specific conductivity (κ).
34. Which of the following statements is not applicable to electrolytic conductors?
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Correct Answer: (a)
In electrolytic conductors, current is carried by migrating ions (both cations and anions traveling in opposite directions) rather than a stream of free electrons, which is characteristic of metallic conductors.
35. The highest electrical conductivity of the following aqueous solutions is of:
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Correct Answer: (a)
Fluorine is a highly electronegative atom. The presence of two electron-withdrawing fluorine atoms in difluoroacetic acid strongly enhances its acid strength through the inductive effect, leading to the highest degree of ionization and conductivity.
36. If the half cell reaction, A + e- → A-, has a large negative reduction potential, it follows that:
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Correct Answer: (c)
A large negative reduction potential indicates that the forward reduction reaction is highly unfavorable, meaning the reverse oxidation reaction (A- → A + e-) proceeds very readily.
37. The specific conductance of 0.1 N KCl solution at 23°C is 0.012 ohm-1 cm-1. The resistance of cell containing the solution at the same temperature was found to be 55 ohm. The cell constant will be:
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Correct Answer: (a)
Formula: Specific Conductance (κ) = Cell Constant / Resistance (R) Cell Constant = κ × R = 0.012 × 55 = 0.66 cm-1.
38. Which of the following reaction is used to make a fuel cell?
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Correct Answer: (a)
The combustion reaction of hydrogen gas with oxygen gas to yield water is the foundational chemical framework utilized in standard hydrogen-oxygen fuel cells.
39. The electrolytic decomposition of dilute sulphuric acid with platinum electrode in cathodic reaction is:
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Correct Answer: (a)
The reaction taking place at the cathode always involves the gain of electrons, which by definition is a reduction reaction (2H+ + 2e- → H2).
40. In electrolysis of dilute H2SO4 using platinum electrodes:
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Correct Answer: (c) [and (a) is also correct contextually]
During electrolysis of dilute H2SO4, H+ ions travel to the cathode and get reduced to evolve Hydrogen gas (H2). Concurrently, water is oxidized at the anode to produce Oxygen gas (O2).
41. Which of the following statements is correct? Galvanic cell converts:
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Correct Answer: (a)
A galvanic (or voltaic) cell is an electrochemical device that converts chemical energy derived from a spontaneous redox reaction into electrical work energy.
42. Consider the galvanic cell Zn | ZnSO4 || CuSO4 | Cu, the reaction at cathode is:
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Correct Answer: (c)
In the Daniell cell, the copper electrode acts as the cathode, where copper ions undergo reduction: Cu2+ + 2e- → Cu.
43. Calculate conductance at infinite dilution of HOAc using appropriate molar conductances of the electrolytes listed below at infinite dilution in H2O at 25°C:
| Electrolyte | KCl | KNO3 | HCl | NaOAc | NaCl |
|---|---|---|---|---|---|
| Λ° (S cm² mol⁻¹) | 149.9 | 145.0 | 426.2 | 91.0 | 126.5 |
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Correct Answer: (b)
According to Kohlrausch's Law:Λ°(HOAc) = Λ°(HCl) + Λ°(NaOAc) - Λ°(NaCl)
Λ°(HOAc) = 426.2 + 91.0 - 126.5 = 390.7 S cm² mol⁻¹.
44. The hydrogen electrode is dipped in a solution of pH = 3 at 25°C. The potential of the cell would be (taking 2.303RT/F as 0.059 V):
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Correct Answer: (d)
The electrode reduction half-reaction is: H+ + e- → 1/2 H2.Using Nernst equation: E = E° - 0.059 log(1/[H+])
E = 0 - 0.059 × pH = -0.059 × 3 = -0.177 V.
45. The standard electrode potential of Zn2+/Zn and Ag+/Ag are -0.763 V and +0.799 V respectively. The standard potential of the cell is:
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Correct Answer: (a)
E°cell = E°cathode (reduction) - E°anode (reduction) Since Ag has the higher reduction potential, it acts as the cathode.
E°cell = 0.799 V - (-0.763 V) = +1.562 V ≈ 1.56 V.
46. Standard electrode potential of NHE (Normal Hydrogen Electrode) at 298 K is:
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Correct Answer: (d)
By universal thermodynamic convention, the standard electrode potential of the standard/normal hydrogen electrode (NHE/SHE) is assigned exactly 0.00 Volts at all temperatures.
47. Four metals A, B, C and D are having respectively standard electrode potentials as -3.05, -1.66, -0.40 and 0.80 V. Which one will be the most reactive?
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Correct Answer: (a)
A lower, more negative standard reduction potential signifies a stronger tendency to lose electrons (undergo oxidation). Metal A has the most negative value (-3.05 V), indicating it is the most reactive reducing agent.
48. For a spontaneous reaction, the ΔG, equilibrium constant (K) and E°cell will be respectively:
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Correct Answer: (a)
For any reaction to proceed spontaneously under standard conditions: 1. Gibbs Free Energy change (ΔG°) must be negative (< 0).
2. Cell potential (E°cell) must be positive (> 0).
3. Equilibrium constant (K) must be greater than 1 (> 1).
49. The standard reduction potential for Fe2+/Fe and Sn2+/Sn electrodes are -0.44 V and -0.14 V respectively. For the given cell reaction: Fe + Sn2+ → Fe2+ + Sn, standard emf is:
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Correct Answer: (a)
In the reaction, Fe is oxidized (Anode) and Sn2+ is reduced (Cathode). E°cell = E°cathode - E°anode = -0.14 V - (-0.44 V) = +0.30 V.
50. Electrode potential of Zn2+/Zn is -0.76 V and that of Cu2+/Cu is +0.34 V. The emf of the cell constructed between these two electrodes is:
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Correct Answer: (a)
E°cell = E°cathode - E°anode Copper acts as the cathode (+0.34 V) and Zinc acts as the anode (-0.76 V).
E°cell = 0.34 - (-0.76) = +1.10 V.
51. Reduction potential of four elements P, Q, R, S is -2.90, +0.34, +1.20 and -0.76 V. Reactivity decreases in the order:
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Correct Answer: (c)
Chemical reactivity for metals is inversely proportional to their reduction potentials. The lower (more negative) the reduction potential, the more reactive the metal. Arranging from lowest to highest potential: P (-2.90) < S (-0.76) < Q (+0.34) < R (+1.20).
Thus, the reactivity decreases in the order: P > S > Q > R.
52. In the electrochemical cell: H2(g) 1 atm | H+(1 M) || Cu2+ (1 M) | Cu(s). Which one of the following statements is true?
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Correct Answer: (a)
According to cell notation convention, the anode half-cell is always written on the left side and the cathode half-cell on the right side. Therefore, the hydrogen electrode is the anode and the copper electrode is the cathode.
53. One of the following is false for Hg:
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Correct Answer: (d)
Mercury (Hg) is positioned below hydrogen in the electrochemical activity series. It has a positive standard reduction potential, meaning it cannot reduce hydrogen ions to evolve hydrogen gas from acids or H2S.
54. For the redox reaction: Zn(s) + Cu2+(0.1 M) → Zn2+(1 M) + Cu(s) taking place in a cell, E°cell is 1.10 V. Ecell for the cell will be (2.303RT/F = 0.0591):
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Correct Answer: (b)
Using Nernst Equation: Ecell = E°cell - (0.0591 / n) × log([Zn2+]/[Cu2+]) Here, number of electrons transferred (n) = 2.
Ecell = 1.10 - (0.0591 / 2) × log(1 / 0.1)
Ecell = 1.10 - (0.0295 × log(10)) = 1.10 - 0.0295 = 1.0705 V ≈ 1.07 V.
55. The oxidation potentials of the following half-cell reactions are given:
Zn → Zn2+ + 2e- E° = +0.76 V
Fe → Fe2+ + 2e- E° = +0.44 V
Fe → Fe2+ + 2e- E° = +0.44 V
What will be the emf of the cell whose cell reaction is Fe2+(aq) + Zn → Zn2+(aq) + Fe?
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Correct Answer: (a)
The reaction displays Zinc undergoing oxidation and Iron ions undergoing reduction.E°cell = Standard Oxidation Potential of Anode (Zn) + Standard Reduction Potential of Cathode (Fe)
E°cell = 0.76 V + (-0.44 V) = +0.32 V.
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