Govt. Exams
Entrance Exams
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).
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).
In dilute H₂SO₄, H⁺ is preferentially reduced over water at the cathode (less negative reduction potential), producing H₂ gas.
Cu²⁺ + 2e⁻ → Cu. Moles of Cu = 3.2/64 = 0.05 mol. Charge = 0.05 × 2 = 0.1 F (since 1 F = 1 mole of electrons).
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.
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⁺.
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.
In molten NaCl electrolysis, Na⁺ is reduced at cathode to Na metal. Cl⁻ is oxidized to Cl₂ at anode. Water is absent, so no oxygen evolution.
Upon dilution, the degree of ionization increases due to reduced ion-ion interactions (interionic forces), leading to more free ions and higher molar conductivity.
When E°cell > 0, the cell reaction is spontaneous. ΔG° = -nFE°cell is negative, indicating spontaneity.
