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ICSE Class 10 · Chemistry · Chapter 6

Electrolysis

5 topics · 20 questions

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Everything you need, in order

Fundamental Definitions and Terminology

  • Electrolysis: The decomposition of a chemical compound (in its molten state or aqueous solution) by passing a direct electric current through it.
  • Electrolyte: A substance that conducts electricity in its molten or aqueous state and is simultaneously decomposed. Examples: Molten NaCl, Aqueous H₂SO₄.
  • Non-electrolyte: A substance that does not conduct electricity in any state. Examples: Sugar (C₁₂H₂₂O₁₁), Alcohol (C₂H₅OH).
  • Electrodes: Conductors (usually metallic or graphite) through which electric current enters and leaves the electrolyte.
  • Anode: Connected to the positive terminal of the battery; site of oxidation (anions move here). Electrons are lost here.
  • Cathode: Connected to the negative terminal of the battery; site of reduction (cations move here). Electrons are gained here.
  • Ions: Charged particles formed when atoms gain or lose electrons. Cations (positive ions) move to cathode, Anions (negative ions) move to anode.

Mechanism and Redox Reactions

  • The Redox Nature: Electrolysis is fundamentally a redox (reduction-oxidation) reaction driven by electrical energy.
  • Oxidation at Anode: Loss of electrons occurs at the anode. Anions discharge by losing electrons. Example: 2Cl⁻ → Cl₂ + 2e⁻
  • Reduction at Cathode: Gain of electrons occurs at the cathode. Cations discharge by gaining electrons. Example: Cu²⁺ + 2e⁻ → Cu
  • Ion Movement: In the electrolyte, cations migrate towards the cathode (negative electrode) and anions migrate towards the anode (positive electrode).
  • Discharge of Ions: The process where ions gain or lose electrons at the electrodes to form neutral atoms or molecules.

Electrochemical Series and Selective Discharge

  • Electrochemical Series for Cations (Decreasing order of discharge preference):
  • Ag⁺ > Hg²⁺ > Cu²⁺ > H⁺ > Pb²⁺ > Sn²⁺ > Ni²⁺ > Zn²⁺ > Al³⁺ > Mg²⁺ > Na⁺ > Ca²⁺ > K⁺
  • Electrochemical Series for Anions (Decreasing order of discharge preference):
  • SO₄²⁻ < NO₃⁻ < OH⁻ < Cl⁻ < Br⁻ < I⁻
  • Factors Affecting Selective Discharge:
  • 1. Position in Electrochemical Series: Lower in series = easier to discharge
  • 2. Concentration: Higher concentration favors discharge (e.g., concentrated Cl⁻ over OH⁻)
  • 3. Nature of Electrode: Active electrodes participate in reactions; Inert electrodes (Pt, C) don't react

Important Examples

  • Electrolysis of Molten Lead Bromide (PbBr₂):
  • • At Cathode: Pb²⁺ + 2e⁻ → Pb (lead metal deposited)
  • • At Anode: 2Br⁻ → Br₂ + 2e⁻ (bromine gas evolved)
  • • Overall: PbBr₂ → Pb + Br₂
  • Electrolysis of Acidified Water (H₂SO₄ added):
  • • At Cathode: 2H⁺ + 2e⁻ → H₂ (hydrogen gas)
  • • At Anode: 4OH⁻ → 2H₂O + O₂ + 4e⁻ (oxygen gas)
  • • Volume ratio H₂ : O₂ = 2 : 1
  • • Acid is added to increase conductivity and provide H⁺ ions
  • Electrolysis of Aqueous Copper Sulphate (CuSO₄):
  • • With Inert Electrodes (Pt/Graphite):
  • - Cathode: Cu²⁺ + 2e⁻ → Cu (copper deposited)
  • - Anode: 4OH⁻ → 2H₂O + O₂ + 4e⁻ (oxygen evolved)
  • • With Active Copper Electrodes:
  • - Cathode: Cu²⁺ + 2e⁻ → Cu (pure copper deposited)
  • - Anode: Cu → Cu²⁺ + 2e⁻ (impure copper dissolves)
  • - Used for electro-refining of copper

Applications of Electrolysis

  • Electroplating: Coating one metal with another using electrolysis.
  • • Object to be plated = Cathode
  • • Plating metal = Anode
  • • Electrolyte contains ions of plating metal
  • • Uses: Silver plating, Gold plating, Chromium plating
  • • Advantages: Corrosion resistance, improved appearance, durability
  • Electro-refining: Purification of metals using electrolysis.
  • • Impure metal = Anode (dissolves)
  • • Pure metal = Cathode (deposits)
  • • Example: Copper refining using CuSO₄ solution
  • • Impurities settle as anode mud
  • Industrial Applications:
  • • Production of hydrogen and oxygen from water
  • • Extraction of reactive metals (Na, Mg, Al)
  • • Production of chlorine and sodium hydroxide
  • • Electroplating industry

Quiz

Test your knowledge

Multiple choice

  1. Question 1 of 15Knowledge
    Electrolysis is the decomposition of a compound by:
  2. Question 2 of 15Knowledge
    At which electrode does oxidation occur?
  3. Question 3 of 15Knowledge
    Which of the following is a non-electrolyte?
  4. Question 4 of 15Knowledge
    In the electrolysis of molten PbBr₂, what is produced at the cathode?
  5. Question 5 of 15Knowledge
    The volume ratio of hydrogen to oxygen in electrolysis of water is:
  6. Question 6 of 15Knowledge
    Which ion will be discharged first at the cathode from a mixture of Cu²⁺ and Zn²⁺?
  7. Question 7 of 15Knowledge
    In electroplating, the object to be plated acts as:
  8. Question 8 of 15Application
    Acid is added to water during electrolysis to:
  9. Question 9 of 15Knowledge
    Which of the following will be discharged first at the anode?
  10. Question 10 of 15Knowledge
    The process of purifying metals using electrolysis is called:
  11. Question 11 of 15Knowledge
    In electrolysis of CuSO₄ with copper electrodes, what happens to the mass of the anode?
  12. Question 12 of 15Application
    Which gas is evolved at the anode during electrolysis of dilute H₂SO₄?
  13. Question 13 of 15Knowledge
    The electrode connected to the negative terminal of the battery is called:
  14. Question 14 of 15Knowledge
    Which factor does NOT affect selective discharge of ions?
  15. Question 15 of 15Knowledge
    In the electrolysis of brine (concentrated NaCl), which gas is produced at the anode?

Practice numericals

  1. Problem 1 of 5Knowledge
  2. Problem 2 of 5Knowledge
  3. Problem 3 of 5Application
  4. Problem 4 of 5Knowledge
  5. Problem 5 of 5Knowledge

0 of 20 answered