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Electrochemistry – Class 12 Chemistry notes, important questions and MCQs

NCERT Class 12 Chemistry, chapter 2. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Electrochemistry links chemical reactions with electricity: galvanic cells produce current, electrolytic cells use current to drive reactions.

Cells and potentials

Galvanic cell: oxidation at anode (−), reduction at cathode (+); E°cell = E°cathode − E°anode.
Standard hydrogen electrode has E° = 0 V.
Nernst equation: E = E° − (0.059/n) log Q at 298 K; ΔG° = −nFE°cell.

Conductance and electrolysis

Molar conductivity Λm = κ × 1000/M; increases on dilution (Kohlrausch's law for limiting values).
Faraday's first law: m = ZIt; 1 F = 96,500 C mol⁻¹.
Batteries: dry cell, lead storage, fuel cells (H₂–O₂); corrosion is an electrochemical process.

Key terms

Electrode potential: tendency of an electrode to lose or gain electrons
Faraday constant: charge on one mole of electrons, 96,500 C
Kohlrausch's law: limiting molar conductivity of an electrolyte is the sum of the limiting ionic conductivities of its ions

Formulas

E°cell = E°cathode − E°anode
ΔG° = −nFE°
E = E° − (0.059/n) log Q
m = ZIt

Important questions with answers

Why does molar conductivity increase on dilution?2 marks

On dilution, ions move more freely (weaker interionic attractions) and, for weak electrolytes, the degree of dissociation increases, so the conductance per mole of electrolyte rises.

Write the Nernst equation for a Daniell cell and state what happens to E as [Zn²⁺] increases.3 marks

Zn + Cu²⁺ → Zn²⁺ + Cu, n = 2. E = E° − (0.0591/2) log([Zn²⁺]/[Cu²⁺]) at 298 K. Increasing [Zn²⁺] increases the log term, so E decreases.

State Faraday's laws of electrolysis. A current of 2 A is passed through CuSO₄ solution for 30 minutes. Find the mass of copper deposited (Cu = 63.5 g/mol). Also explain why hydrogen fuel cells are better than burning fuel.5 marks

First law: mass deposited is proportional to the charge passed (m = ZQ). Second law: for the same charge, masses of different substances are proportional to their equivalent weights. Q = 2 × 1800 = 3600 C. Cu²⁺ + 2e⁻ → Cu needs 2F = 193,000 C per 63.5 g. m = 3600 × 63.5/193,000 ≈ 1.18 g. Fuel cells convert chemical energy directly into electricity with about 60–70% efficiency (higher than heat engines), and the H₂–O₂ cell produces only water, so there is no pollution.

Quick revision

Anode: oxidation; cathode: reduction.
SHE potential is zero.
Molar conductivity rises on dilution.

Exam tips

A positive E°cell means the reaction is spontaneous (ΔG negative).
E°cell = E°cathode − E°anode (both reduction potentials); a positive E°cell means the cell reaction is spontaneous.

Practice MCQs

Oxidation occurs at the
1. cathode
2. anode
3. salt bridge
4. both electrodes
Show answer
Answer: (b) anode. Anode.
The value of 1 faraday is about
1. 96,500 C
2. 9650 C
3. 1.6 × 10⁻¹⁹ C
4. 6.022 × 10²³ C
Show answer
Answer: (a) 96,500 C. Charge of 1 mol electrons.
E° of Zn²⁺/Zn = −0.76 V and Cu²⁺/Cu = +0.34 V. E°cell of Daniell cell is
1. 0.42 V
2. 1.10 V
3. −1.10 V
4. 0.34 V
Show answer
Answer: (b) 1.10 V. 0.34 − (−0.76).
For a spontaneous cell reaction
1. ΔG > 0, E > 0
2. ΔG = 0
3. ΔG < 0, E < 0
4. ΔG < 0, E > 0
Show answer
Answer: (d) ΔG < 0, E > 0. ΔG = −nFE.
Charge needed to deposit 1 mol of Al from Al³⁺ is
1. 1 F
2. 2 F
3. 3 F
4. 6 F
Show answer
Answer: (c) 3 F. Al³⁺ + 3e⁻.
Charge needed to deposit 1 mol of Al from Al³⁺ is
1. 1 F
2. 2 F
3. 3 F
4. 6 F
Show answer
Answer: (c) 3 F. Three electrons per ion.
The fuel cell used in Apollo missions used
1. methane and oxygen
2. zinc and carbon
3. hydrogen and oxygen
4. lead and acid
Show answer
Answer: (c) hydrogen and oxygen. H₂–O₂ cell.
For a cell with E°cell = 1.1 V and n = 2, ΔG° is about
1. −212 kJ
2. −106 kJ
3. −53 kJ
4. +212 kJ
Show answer
Answer: (a) −212 kJ. −nFE° = −2 × 96500 × 1.1.

All chapters of Class 12 Chemistry

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.