Electrolysis Comprehensive Notes

Key Concepts of Electrolysis

• Electrolysis Definition

  • Electrolysis is the splitting of substances using electricity with the following key components:
  • Electrolyte: the ionic compound being broken down, existing in molten state or aqueous solution.
  • Electric Current: drives the process of decomposition.

• Ionic Compounds

  • Conduct electricity due to charged particles (ions) present.
  • Ions can only move freely when the compounds are dissolved (aqueous) or molten.

• Electrolytic Cell Components

  • Electrodes: Conductors where the reactions occur.
  • Cathode (Negative Electrode): attracts cations (positive ions).
  • Anode (Positive Electrode): attracts anions (negative ions).
  • Charge Carriers:
  • In wires, charge is carried by electrons.
  • In electrolytes, charge is carried by ions.

Process of Electrolysis

• Ion Formation During Electrolysis
  • Metals form cations (positive) by losing electrons.
  • Non-metals form anions (negative) by gaining electrons.
• Key Reactions:
  • Reaction at the Cathode (Reduction):
  • Cations gain electrons to form neutral atoms, e.g., ext{A}^{3+} + 3e^-
    ightarrow ext{A}.
  • Reaction at the Anode (Oxidation):
  • Anions lose electrons to form neutral atoms or molecules, e.g., 2 ext{Cl}^-
    ightarrow ext{Cl}_2 + 2e^-.

Key Reactions in Electrolysis of Specific Compounds

• Aluminium Oxide Electrolysis:

  • Dissolved in molten cryolite to improve conductivity.
  • Products:
  • Cathode: ext{Al}^{3+} + 3e^-
    ightarrow ext{Al (l)}
  • Anode: 2 ext{O}^{2-}
    ightarrow ext{O}_2(g) + 4e^-
  • Oxygen reacts with graphite anodes to produce carbon dioxide.

• Electrolysis of Sodium Chloride Solution:

  • Products:
  • Cathode: Hydrogen gas (H₂) when sodium ions (Na⁺) are above hydrogen in the reactivity series.
  • Anode: Chlorine gas (Cl₂) is produced due to chloride ions (Cl⁻) discharge.
  • Half-equations:
  • Cathode: 2 ext{H}^+ + 2e^-
    ightarrow ext{H}_2(g)
  • Anode: 2 ext{Cl}^-
    ightarrow ext{Cl}_2(g) + 2e^-

Rules for Products in Electrolysis

• At the Cathode:
  • If the metal is more reactive than hydrogen, hydrogen will be produced.
  • If the metal is less reactive, the metal will be deposited.
• At the Anode:
  • If halide ions are present, the corresponding halogen is produced.
  • If no halide ions, oxygen is produced from hydroxide ions.

Additional Notes on Half Equations

• Oxidation (At Anode): Losing electrons, e.g., ext{4OH}^-
  ightarrow ext{O}2(g) + 2 ext{H}2 ext{O}(l) + 4e^-
• Reduction (At Cathode): Gaining electrons, e.g., ext{Zn}^{2+} + 2e^-
  ightarrow ext{Zn}
• Summary of Reactions:
  • Identify ions and their reactions based on their charge and the electrode they are attracted to.

Example Reactions for Different Electrolytes

Summary of Learning Objectives

• Understand the Process of Electrolysis:

  • Importance of ions, electrodes, and electric current in decomposition reactions.

• Predicting Products of Electrolysis:

  • Use the reactivity series to determine what will occur at anode and cathode.