ICSE Class 10 Chemistry: Electrolysis — Complete Notes 2026

Electrolysis — Basic Concepts

• Electrolyte: substance that conducts electricity in molten/aqueous state via ions
• Electrolytic cell: anode (+), cathode (−), electrolyte, external DC source
• Discharge of ions: cations move to cathode, anions to anode

Preferential Discharge of Ions

• When mixture of ions present, the ion discharged depends on: concentration, electrode material, position in electrochemical series
• Chlorine preferentially discharged over OH⁻ in concentrated NaCl solution
• Cu²⁺ discharged over H⁺ because Cu is below H in electrochemical series

Electrolysis of Water (dilute H₂SO₄)

• Cathode: 4H⁺ + 4e⁻ → 2H₂; volume 2 units
• Anode: 2H₂O → O₂ + 4H⁺ + 4e⁻; volume 1 unit
• Hydrogen:Oxygen ratio = 2:1 by volume

Electrolysis of Brine (NaCl solution)

• Cathode product: H₂ gas; Anode product: Cl₂ gas
• Remaining solution: NaOH (caustic soda)
• Industrial applications: chlor-alkali process; products used in PVC, bleach, detergents

Electrolysis of CuSO₄ solution

• With carbon electrodes: cathode deposits Cu; anode releases O₂; solution becomes dilute H₂SO₄
• With copper electrodes: cathode gains Cu; anode dissolves Cu; concentration unchanged
• Used in electrorefining of copper: pure Cu deposited at cathode

Faraday's Laws of Electrolysis

• First law: mass deposited ∝ charge passed; m = ZIt where Z is electrochemical equivalent
• Second law: masses deposited by same charge ∝ equivalent weight
• Calculation: 96500 C deposits 1 gram-equivalent (1 Faraday)

Electroplating

• Process of depositing a thin layer of metal on an object by electrolysis
• Object to be plated = cathode; metal to be deposited = anode; salt of that metal = electrolyte
• Applications: chromium plating of car parts, silver plating of cutlery, zinc galvanising