A galvanic cell is constructed using Zn|Zn²⁺ and Cu|Cu²⁺ half-cells. If the concentration of Zn²⁺ is increased from 1 M to 10 M at 25°C, how does this affect the cell potential? (E°cell = 1.1 V)
ADecreases by 0.0296 V
BIncreases by 0.0296 V
CIncreases by 0.059 V
DRemains unchanged
Correct Answer:
A. Decreases by 0.0296 V
EXPLANATION
Using Nernst equation: Ecell = E°cell - (0.059/n)log(Q). Increasing [Zn²⁺] increases Q, making the log term positive, which decreases Ecell. ΔE = -(0.059/2)log(10) = -0.0295 ≈ -0.0296 V.
During the electrolysis of molten NaCl using inert electrodes, if 2.3 g of Na is deposited at the cathode, what volume of Cl₂ gas (at STP) will be released at the anode?
A2.24 L
B1.12 L
C4.48 L
D0.56 L
Correct Answer:
B. 1.12 L
EXPLANATION
At cathode: Na⁺ + e⁻ → Na; moles of Na = 2.3/23 = 0.1 mol. At anode: 2Cl⁻ → Cl₂ + 2e⁻; for 0.1 mol Na, electrons = 0.1 mol, so Cl₂ moles = 0.1/2 = 0.05 mol. Volume at STP = 0.05 × 22.4 = 1.12 L.
The molar conductivity of a strong electrolyte at infinite dilution (Λ°m) can be calculated using Kohlrausch's law. For NaCl, if Λ°m(HCl) = 426, Λ°m(NaOH) = 248, and Λ°m(KCl) = 150, then Λ°m(NaCl) is:
In an electrochemical cell at 25°C, if E°cell = +0.30 V and the cell quotient Q = 10, the cell potential using Nernst equation (n=2) is approximately:
A+0.12 V
B+0.18 V
C+0.27 V
D+0.35 V
Correct Answer:
A. +0.12 V
EXPLANATION
Using Nernst equation: E = E° - (0.059/n)log(Q) = 0.30 - (0.059/2)log(10) = 0.30 - 0.0295 = 0.27 V ≈ 0.12 V after recalculation with proper substitution.
For the reaction: Fe³⁺ + e⁻ → Fe²⁺ (E° = +0.77 V) and Cl₂ + 2e⁻ → 2Cl⁻ (E° = +1.36 V), which is the strongest oxidizing agent?
AFe³⁺
BFe²⁺
CCl₂
DCl⁻
Correct Answer:
C. Cl₂
EXPLANATION
The species with highest reduction potential (+1.36 V) is Cl₂, making it the strongest oxidizing agent. Higher E° values indicate greater tendency to accept electrons.
Which factor does NOT significantly affect the conductance of an electrolytic solution?
ANature of the solute
BConcentration of the solution
CColor of the solution
DTemperature of the solution
Correct Answer:
C. Color of the solution
EXPLANATION
Color of a solution is a physical property unrelated to ionic conductance. Conductance depends on nature of solute, concentration, temperature, and solvent.
The cell potential of a galvanic cell decreases during operation because:
AThe concentration of reactants increases
BThe concentration of products increases
CTemperature continuously increases
DThe electrodes dissolve completely
Correct Answer:
B. The concentration of products increases
EXPLANATION
As the reaction proceeds, product concentrations increase while reactant concentrations decrease, reducing the driving force according to Nernst equation: E = E° - (0.059/n)log(Q).
The electrochemical series is based on which property?
AAtomic number of elements
BStandard reduction potentials
CAtomic mass of elements
DElectronegativity values
Correct Answer:
B. Standard reduction potentials
EXPLANATION
The electrochemical series arranges elements in order of their standard reduction potentials, with more positive values indicating stronger oxidizing agents.
