Electrolysis of Ionic Compounds

Learning Objectives

• Explain why ionic compounds can conduct electricity when molten or dissolved in water.
• Describe the reactions at positive and negative electrodes during electrolysis.
• Identify reactions as reduction or oxidation (higher tier).

Overview of Electrolysis

• Topic will be divided into multiple videos for clarity.
• Focus of this video: General ideas of electrolysis.

Ionic Compounds Recap

• Example: Lead bromide (PbBr2)
  • Formed when lead (Pb) reacts with bromine (Br).
  • Lead atom loses two electrons, forming a lead ion (Pb²⁺).
  • Electrons are gained by bromine atoms, forming bromide ions (Br⁻).

Key Facts about Electrolysis

• Solid Ionic Compounds

  • Cannot conduct electricity due to locked ions.
  • Ions are in a regular pattern, held by strong electrostatic forces.

• When Molten or Dissolved

  • Forces of attraction are broken.
  • Ions are free to move, allowing conduction of electricity.
  • These are called electrolytes.

Electrolysis of Molten Lead Bromide

• Ions Present:

  • Positive lead ions (Pb²⁺)
  • Negative bromide ions (Br⁻)

• Electrodes:

  • Negative Electrode (Cathode):
    • Attached to negative terminal of power supply.
    • Covered with electrons.
  • Positive Electrode (Anode):
    • Connected to positive terminal.
    • Lacks electrons.

• Reactions:

  • At the Cathode:
    • Lead ions (Pb²⁺) gain electrons to form lead atoms.
    • This is a reduction reaction (gain of electrons).
  • At the Anode:
    • Bromide ions (Br⁻) lose electrons to form bromine atoms.
    • Bromine atoms pair to form Br₂ molecules.
    • This is an oxidation reaction (loss of electrons).

Upcoming Topics

• Next video: Electrolysis to extract reactive metals like aluminium.
• Additional resources available in the revision workbook.

Conclusion

• Ionic compounds conduct electricity when molten/dissolved due to free-moving ions.
• Reactions at electrodes involve reduction at cathode and oxidation at anode.