⚡ CBSE · Class 12 · Chemistry · Chapter 3

Electro-
chemistry

Complete chapter resources for CBSE Class 12 Chemistry — topic breakdown, key formulas (Nernst equation, Faraday's laws, Kohlrausch's law), sample questions, previous year board questions, and instant AI question paper generation.

5Topics
6–8Board marks
8Sample questions
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Key Formulas — Chapter 3
  • Nernst equation: E_cell = E°_cell − (0.0592/n) log Q (at 298 K)
  • Cell EMF: E°_cell = E°_cathode − E°_anode
  • Gibbs–cell relation: ΔG° = −nFE°_cell
  • Faraday's 1st law: w = (M / nF) × I × t
  • Molar conductivity: Λm = (κ × 1000) / M
  • Kohlrausch's law: Λ°m = Σ λ°(cations) + Σ λ°(anions)
Chapter Overview

What this chapter covers

Electrochemistry is the branch of chemistry that studies the interconversion of chemical energy and electrical energy. Chapter 3 of NCERT Class 12 Chemistry covers two types of electrochemical cells: galvanic (voltaic) cells, which spontaneously produce electrical energy from redox reactions (e.g. the Daniell cell), and electrolytic cells, where an external electrical source drives a non-spontaneous redox reaction such as the electrolysis of water or brine.

A major focus is the Nernst equation, which relates the EMF of a cell to the standard electrode potential and the reaction quotient Q. At 298 K it reduces to E_cell = E°_cell − (0.0592/n) log Q. The chapter also develops the concept of molar conductivity (Λm) and its variation with concentration — Kohlrausch's law of independent migration of ions gives Λ°m at infinite dilution, enabling the calculation of the degree of dissociation and dissociation constant for weak electrolytes.

Board questions consistently test Faraday's laws of electrolysis (mass deposited, charge passed, and stoichiometric calculations), cell notation and half-reactions, and numerical problems combining the Nernst equation with Gibbs free energy (ΔG° = −nFE°). Understanding the distinction between conductance, conductivity, and molar conductivity, and how each changes with dilution, is essential for scoring full marks in this chapter.

Topics

What's inside Chapter 3

As per NCERT Class 12 Chemistry (CBSE syllabus)

Topic 1
Electrochemical Cells & Cell EMF
Galvanic vs electrolytic cells. Cell notation (anode || cathode). Standard hydrogen electrode (SHE). Standard electrode potentials (E°) and the electrochemical series. Calculation of E°_cell from half-cell E° values.
Topic 2
Nernst Equation & Cell Thermodynamics
Nernst equation at any temperature and at 298 K. Relation to Gibbs free energy: ΔG° = −nFE°_cell. Equilibrium constant K from E°_cell. Effect of concentration on cell potential.
Topic 3
Conductance of Electrolytic Solutions
Resistance, conductance, conductivity (κ), and molar conductivity (Λm). Variation of Λm with concentration for strong and weak electrolytes. Kohlrausch's law: Λ°m = Σ λ°(ions). Degree of dissociation and Ka from conductance data.
Topic 4
Electrolysis & Faraday's Laws
Electrolysis of molten NaCl, aqueous NaCl (brine), and water. Faraday's First Law: w = ZIt. Faraday's Second Law: masses proportional to equivalent weights. Calculations involving charge, current, time, and moles of product.
Topic 5
Batteries, Fuel Cells & Corrosion
Primary cells (dry cell, mercury cell) vs secondary cells (lead storage battery, Ni-Cd). Hydrogen-oxygen fuel cells. Electrochemical theory of corrosion: iron rusting as a galvanic process; protection methods (cathodic protection, galvanising).
Connections

How this chapter fits in

Useful for setting question difficulty and cross-chapter papers.

Builds on
Ch 1 · The Solid State
Ionic lattice structures underpin ionic conductor behaviour
Class 11 Redox Reactions
Oxidation states, half-reactions, and balancing redox equations
Chapter 3 Electro-
chemistry
Leads to
Ch 4 · Chemical Kinetics
Rate constants and activation energy link to ΔG° concepts
Industrial Chemistry (Class 12)
Electroplating, chlor-alkali process, Hall-Heroult process
Board Blueprint

Marks & question-type breakdown

Typical pattern based on CBSE Class 12 Chemistry board papers from the last five years.

Question type Marks Typical count What's usually tested
MCQ / Assertion-Reason 1 1–2 Electrochemical series, cell notation, Faraday's constant value
Very Short Answer 2 1 Molar conductivity calculation or Kohlrausch's law application
Short Answer 3 1 Nernst equation numerical or Faraday's law mass-deposited problem
Long Answer / Case-Based 4–5 1 Cell EMF + ΔG° + K combined, or electrolysis multi-part problem
Total (approximate) 6–8 4–5 Weightage varies across paper sets and years
Sample Questions

8 sample questions — generated by MarksZen AI

Aligned to CBSE Class 12 Chemistry Chapter 3. Covers all question types across Easy, Medium, and Hard difficulty.

Q1 Easy 1 mark MCQ
In a galvanic cell, oxidation takes place at the: (a) Cathode (b) Anode (c) Salt bridge (d) Both electrodes
Q2 Easy 2 marks Short Answer
The conductivity of a 0.20 M solution of KCl at 298 K is 0.025 S cm⁻¹. Calculate its molar conductivity.
Q3 Medium 2 marks Short Answer
Calculate the standard cell potential (E°_cell) for the following cell and determine whether the reaction is spontaneous: Zn | Zn²⁺ || Cu²⁺ | Cu Given: E°(Zn²⁺/Zn) = −0.76 V, E°(Cu²⁺/Cu) = +0.34 V
Q4 Medium 3 marks Short Answer
Using the Nernst equation, calculate the EMF of the following cell at 298 K: Mg | Mg²⁺ (0.001 M) || Cu²⁺ (0.0001 M) | Cu Given: E°(Mg²⁺/Mg) = −2.37 V, E°(Cu²⁺/Cu) = +0.34 V
Q5 Medium 3 marks Short Answer
The molar conductivity of a weak acid HA at concentration c is Λm. Its limiting molar conductivity is Λ°m. Derive an expression for the degree of dissociation (α) and the acid dissociation constant Ka in terms of Λm, Λ°m, and c.
Q6 Hard 4 marks Word Problem
How many grams of aluminium are deposited when a current of 2.5 A is passed through an aqueous solution of AlCl₃ for 1 hour? (Given: Atomic mass of Al = 27 g mol⁻¹, Faraday constant F = 96500 C mol⁻¹)
Q7 Hard 4 marks Word Problem
Calculate the standard Gibbs free energy (ΔG°) and the equilibrium constant (K) at 298 K for the cell reaction: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s) Given: E°_cell = +1.10 V, F = 96500 C mol⁻¹, R = 8.314 J K⁻¹ mol⁻¹
Q8 Hard 5 marks Case-Based
A lead storage battery discharges at a steady current of 3 A for 12 hours. (i) Calculate the total charge (in coulombs) that flows through the circuit. (ii) How many moles of PbSO₄ are formed at the anode? (Pb²⁺ requires 2 electrons) (iii) What is the mass of PbSO₄ deposited? (Molar mass of PbSO₄ = 303 g mol⁻¹) (iv) How does recharging restore the original cell composition?
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Previous Year Questions

From CBSE board examinations

Actual questions from past Class 12 Chemistry board papers — Electrochemistry chapter.

Board 20223 marks
Calculate the emf of the following cell at 298 K: Fe | Fe²⁺ (0.001 M) || H⁺ (1 M) | H₂ (g) (1 bar) | Pt Given: E°(Fe²⁺/Fe) = −0.44 V. (All India 2022)
Board 20232 marks
The molar conductivity of CH₃COOH at infinite dilution is 390.5 S cm² mol⁻¹. If the molar conductivity of a 0.1 M acetic acid solution is 5.20 S cm² mol⁻¹, calculate the degree of dissociation. (Delhi 2023)
Board 20205 marks
A copper electrode is used in the electrolysis of an aqueous CuSO₄ solution. A current of 5 A is passed for 965 seconds. (a) Write the half-reactions at the anode and cathode. (b) Calculate the mass of copper deposited at the cathode. (c) What volume of O₂ gas is liberated at the anode at STP? (Atomic mass: Cu = 63.5 g mol⁻¹; F = 96500 C mol⁻¹) (CBSE 2020)
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FAQ

Questions teachers ask

How many marks does Electrochemistry carry in the CBSE Class 12 board exam? +
Electrochemistry typically carries 6–8 marks in the CBSE Class 12 Chemistry board paper. Questions appear as one 1-mark MCQ or assertion-reason, one 2-mark short answer (often on conductance or EMF), and one 3–5 mark problem involving the Nernst equation or Faraday's laws. The chapter has appeared in every CBSE board paper for over a decade.
What is the Nernst equation and how is it applied in board exam questions? +
The Nernst equation, E_cell = E°_cell − (RT/nF) ln Q, relates the EMF of an electrochemical cell to the concentrations of its species. At 298 K it simplifies to E_cell = E°_cell − (0.0592/n) log Q. Board questions typically give E°_cell and ion concentrations and ask students to calculate E_cell. These are standard 3–5 mark problems.
What is the difference between molar conductivity and equivalent conductivity in CBSE exams? +
Molar conductivity (Λm) is the conductance of a solution containing 1 mole of electrolyte between two electrodes, while equivalent conductivity uses the gram-equivalent. NCERT Class 12 focuses on molar conductivity. Key relationships: Λm = κ × 1000/M (where κ is conductivity and M is molarity). Kohlrausch's law gives Λ°m as the sum of individual ionic molar conductivities.
How should students approach Faraday's law calculations in board exams? +
Faraday's First Law states that the mass deposited (w) = Z × I × t, where Z is the electrochemical equivalent. Faraday's Second Law states that masses deposited by the same charge are proportional to equivalent weights. For board questions, use w = (M/nF) × I × t directly. Always state the formula, substitute with units, and show the final answer with units for full marks.
How do I generate a custom question paper for Electrochemistry using MarksZen? +
Sign up for a free MarksZen account, choose CBSE Class 12 Chemistry, select Chapter 3 (Electrochemistry), set your preferred question-type mix (MCQ, short answer, numerical) and total marks — the AI generates a complete board-aligned paper with answer key in under 2 minutes, ready for PDF export.