CBSE Class 12 Chemistry: Electrochemistry — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: Derive the Nernst equation. Calculate the EMF of a Daniell cell when [Zn²⁺] = 0.1 M and [Cu²⁺] = 0.01 M.
  Ans: Nernst equation relates EMF to concentration: E = E° - (RT/nF)ln Q. At 25°C: E = E° - (0.0591/n)log Q. For Daniell cell: Zn|Zn²⁺||Cu²⁺|Cu. E° = +1.10 V, n = 2. Q = [Zn²⁺]/[Cu²⁺] = 0.1/0.01 = 10. E = 1.10 - (0.0591/2)log(10) = 1.10 - 0.02955 = 1.07 V.
• Q: Differentiate between electrolytic cell and galvanic cell.
  Ans: Galvanic (Voltaic) cell: Converts chemical energy to electrical energy (spontaneous reaction). Anode is negative, cathode is positive. Example: Daniell cell. Salt bridge connects half-cells. E° is positive. Electrolytic cell: Converts electrical energy to chemical energy (non-spontaneous). Anode is positive, cathode is negative. External battery drives the reaction. Both electrodes dip in same solution. Example: electrolysis of NaCl.
• Q: State Faraday's laws of electrolysis.
  Ans: First Law: Mass of substance deposited ∝ charge passed. m = ZIt = ZQ (Z = electrochemical equivalent). Second Law: When same charge passes through different electrolytes, masses deposited are proportional to their equivalent weights. m₁/m₂ = E₁/E₂. One Faraday (96485 C) deposits one gram equivalent of any substance. For Cu²⁺: 2F deposits 1 mol = 63.5 g.

Long Answer / Application Questions (4-6 Marks)

• Q: Define molar conductivity. How does it vary with concentration for strong and weak electrolytes?
  Ans: Molar conductivity (Λm) = conductivity (κ) × 1000/concentration(M). Unit: S cm² mol⁻¹. Strong electrolytes: Λm increases slightly with dilution (ions separate, less interionic attraction). Kohlrausch's law applies: Λ°m = λ°₊ + λ°₋. Weak electrolytes: Λm increases sharply with dilution (more dissociation occurs). At infinite dilution, dissociation is complete. Degree of dissociation α = Λm/Λ°m.

Exam Tips for This Chapter

• Revise all definitions and laws from Electrochemistry — commonly asked as 1-2 mark questions
• Practice diagrams related to Electrochemistry — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Electrochemistry carries significant marks in the board exam