Which statement is correct regarding electrode potentials?
Answer: B
By international convention, the standard reduction potential of H⁺/H₂ couple is taken as 0.00 V at 25°C. This serves as the reference electrode for all other electrode potentials.
Q.42Easy
For a spontaneous electrochemical cell, the cell potential (E°cell) should be:
Answer: C
For a spontaneous cell reaction, E°cell > 0 (positive). When E°cell is negative, the reaction is non-spontaneous. E°cell = E°cathode - E°anode.
Q.43Medium
The Nernst equation relates cell potential to which of the following?
Answer: C
The Nernst equation: E = E° - (RT/nF)ln(Q) shows that cell potential depends on both temperature (T) and concentration (through Q, the reaction quotient).
Q.44Medium
In the electrolysis of aqueous KCl solution with inert electrodes, which gas is produced at the cathode?
Answer: B
At the cathode in KCl solution, H⁺ ions (from water) are preferentially reduced to H₂ gas because water reduction potential (-0.83 V) is higher than K⁺ reduction potential (-2.93 V).
Q.45Medium
The cell potential at 25°C for the reaction: Cu(s) + 2Ag⁺(aq) → Cu²⁺(aq) + 2Ag(s) is 0.46 V. Calculate ΔG°:
Answer: B
ΔG° = -nFE°cell = -2 × 96485 × 0.46 = -88,766 J/mol ≈ -88.7 kJ/mol. The negative value confirms spontaneity.
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Q.46Medium
Which metal cannot be obtained by electrolysis of its aqueous salt solution?
Answer: C
Sodium has a very negative reduction potential (-2.71 V). Water is preferentially reduced instead. Sodium is obtained by electrolysis of molten NaCl. Copper, silver, and gold can be obtained from aqueous solutions.
Q.47Medium
In a concentration cell with two zinc electrodes in different concentrations of Zn²⁺, which statement is true?
Answer: D
In a concentration cell: E°cell = 0 (identical electrodes), electrodes are chemically identical but in different concentrations, and cell potential depends on concentration difference via Nernst equation.
Q.48Medium
The molar conductivity of a solution decreases with dilution for:
Answer: C
Molar conductivity (Λm) decreases with dilution for both strong and weak electrolytes, but the decrease is greater for weak electrolytes due to increased ionization upon dilution.
Q.49Medium
What is the purpose of a salt bridge in an electrochemical cell?
Answer: B
A salt bridge completes the internal circuit and allows ion migration to maintain electrical neutrality as electrons flow through the external circuit. This prevents charge accumulation.
Q.50Medium
For the electrode reaction: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O, the number of electrons transferred in the redox reaction is:
Answer: C
The equation explicitly shows that 5 electrons (5e⁻) are transferred in this reduction half-reaction where Mn goes from +7 to +2 oxidation state.
Q.51Medium
Using the data: E°(Cu²⁺/Cu) = +0.34 V, E°(Zn²⁺/Zn) = -0.76 V, what is E°cell for the Daniell cell?
Answer: A
E°cell = E°cathode - E°anode = 0.34 - (-0.76) = 0.34 + 0.76 = 1.10 V. Zinc is oxidized (anode) and copper is reduced (cathode).
Q.52Medium
In electroplating of iron with copper, which electrode should be made of copper?
Answer: B
The anode is made of copper (the plating metal) which gets oxidized and dissolved, while the cathode (iron object) receives Cu²⁺ ions that are reduced to form the copper coating.
Q.53Hard
At 25°C, the relationship between ΔG° and K (equilibrium constant) is given by:
Answer: D
ΔG° = -RT ln K and ΔG° = -nFE°cell are both valid relationships. They can be combined as: -nFE° = -RT ln K or nFE° = RT ln K.
Q.54Hard
For the cell: Pt | H₂(1 atm) | H⁺(0.1 M) || Ag⁺(0.1 M) | Ag, calculate E at 25°C if E°cell = 0.80 V and log(0.1) = -1:
Answer: A
Using Nernst: E = E° - (0.059/n)log Q. For this cell, n = 1, Q = [H⁺]/[Ag⁺] = 0.01.1 = 1, log Q = 0. At different concentrations: Q = [H⁺]²/[Ag⁺] = 0.001.1 = 0.1, so E = 0.80 - (0.059)(-1) = 0.859 ≈ 0.82 V
Q.55Hard
The conductivity of a solution is 2.0 × 10⁻⁴ S/cm and the cell constant is 1.0 cm⁻¹. What is the molar conductivity of 0.01 M solution?
Answer: A
Molar conductivity = (κ × 1000)/C = (2.0 × 10⁻⁴ × 1.0 × 1000)/0.01 = 20 S·cm²/mol. where κ is conductivity and C is molarity.
Q.56Hard
In the galvanic cell using Pb-PbSO₄ electrode and Hg-Hg₂Cl₂ electrode (calomel), which is the cathode if E°(Hg₂Cl₂/Hg) = 0.27 V and E°(PbSO₄/Pb) = -0.36 V?
Answer: B
The electrode with higher reduction potential acts as cathode. Since E°(Hg₂Cl₂/Hg) = 0.27 V > E°(PbSO₄/Pb) = -0.36 V, the calomel electrode (Hg-Hg₂Cl₂) is the cathode.
Q.57Medium
What mass of Cu is deposited when 2 Faradays of charge pass through a CuSO₄ solution? (Atomic mass of Cu = 64)
Answer: C
For Cu²⁺ + 2e⁻ → Cu, 2 Faradays deposit 1 mole of Cu. Therefore, 2 Faradays deposit 2 moles of Cu = 2 × 64 = 128 g.
Q.58Easy
In a galvanic cell, the electrode where oxidation occurs is called:
Answer: A
In a galvanic cell, oxidation occurs at the anode (negative electrode), while reduction occurs at the cathode (positive electrode).
Q.59Easy
The standard cell potential (E°cell) for a reaction is -0.45 V at 25°C. What can be concluded about the reaction?
Answer: B
When E°cell is negative, ΔG° = -nFE°cell will be positive, indicating a non-spontaneous reaction under standard conditions.
Q.60Easy
Which of the following is NOT an application of electrochemistry?
Answer: C
Rusting of iron is a corrosion process (galvanic corrosion) and not a direct application like electroplating, electrolysis, or electrorefining.
