Which of the following solutions has the highest conductivity?
Answer: B
HCl is a strong electrolyte with complete ionization. NaCl is also strong but HCl has higher molar conductivity. CH₃COOH and NH₃ are weak electrolytes with low ionization.
Q.162Medium
The equivalent conductivity of a strong electrolyte at infinite dilution (Λ∞) for HCl is approximately:
Answer: A
Λ∞ for HCl ≈ 426 S·cm²·mol⁻¹ (sum of Λ∞H⁺ ≈ 350 and Λ∞Cl⁻ ≈ 76). This is higher than monovalent salts due to high mobility of H⁺.
Q.163Medium
In a concentration cell, the EMF depends on:
Answer: B
In a concentration cell, E°cell = 0, so EMF = (RT/nF)ln(C₁/C₂), depending only on the concentration ratio, temperature, and number of electrons transferred.
Q.164Medium
Calculate the number of Faradays required to deposit 3.2 g of Cu (atomic mass 64) from CuSO₄ solution:
Answer: A
Cu²⁺ + 2e⁻ → Cu. Moles of Cu = 3.642 = 0.05 mol. Charge = 0.05 × 2 = 0.1 F (since 1 F = 1 mole of electrons).
Q.165Medium
In the electrolysis of dilute H₂SO₄ with inert electrodes, the cathode reaction is:
Answer: A
In dilute H₂SO₄, H⁺ is preferentially reduced over water at the cathode (less negative reduction potential), producing H₂ gas.
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Q.166Medium
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.167Medium
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.168Medium
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.
Q.169Medium
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.170Medium
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.171Medium
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.172Medium
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.173Medium
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.174Medium
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.175Medium
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.176Medium
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.177Medium
The molar conductivity of a solution increases with dilution because:
Answer: B
As dilution increases, ions are farther apart, reducing interionic attractions and increasing ionic mobility, thus increasing molar conductivity.
Q.178Medium
For the cell reaction: Zn + Cu²⁺ → Zn²⁺ + Cu, if E°(Zn²⁺/Zn) = -0.76 V and E°(Cu²⁺/Cu) = +0.34 V, the standard cell potential is:
Answer: B
E°cell = E°cathode - E°anode = 0.34 - (-0.76) = 0.34 + 0.76 = 1.10 V. Cu²⁺ is reduced (cathode) and Zn is oxidized (anode).
Q.179Medium
When 3 Faradays of charge are passed through a solution of Cu²⁺, how many moles of Cu are deposited?
Answer: B
For Cu²⁺ + 2e⁻ → Cu, 2 moles of electrons (2 Faradays) deposit 1 mole of Cu. Therefore, 3 Faradays deposit 23 = 1.5 moles of Cu.
Q.180Medium
The relationship between standard Gibbs free energy change (ΔG°) and equilibrium constant (K) at 25°C is best represented by:
Answer: D
The fundamental relationship is ΔG° = -RT ln K. Option A is equivalent when converting to log₁₀: ΔG° = -2.303RT log K. Both are correct, but D is the most fundamental form.
