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.342Medium
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.343Medium
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.344Medium
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.345Medium
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.
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Q.346Medium
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.347Medium
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.348Medium
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.349Medium
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.350Hard
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.351Hard
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.352Hard
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.353Hard
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.354Medium
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.355Easy
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.356Easy
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.357Easy
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.
Q.358Easy
The Faraday constant (F) is numerically equal to:
Answer: A
F = N_A × e = 6.022 × 10²³ × 1.602 × 10⁻¹⁹ C = 96485 C/mol, which equals Avogadro's number times the charge of one electron.
Q.359Easy
In the electrochemical series, which metal is most easily oxidized?
Answer: C
Potassium (K) has the most negative standard reduction potential and is most easily oxidized among the given options. The order of ease of oxidation is K > Cu > Ag > Au.
Q.360Medium
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.
