This topic summary covers Knowledge Organiser: Electrolysis of Molten Compounds within Electrolysis of Molten Compounds for GCSE Chemistry. Revise Electrolysis of Molten Compounds in Electrolysis for GCSE Chemistry with 21 exam-style questions and 14 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 11 of 11 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Electrolysis of Molten Compounds
Key Terms
- Cathode — negative electrode (reduction)
- Anode — positive electrode (oxidation)
- Cation — positive ion, moves to cathode
- Anion — negative ion, moves to anode
- Molten — melted; ions free to move
- Half equation — shows electron transfer at one electrode
Must-Know Facts
- Solid ionic compounds do NOT conduct electricity
- Molten compounds conduct — ions are free
- Cathode (−): cations gain electrons → METAL
- Anode (+): anions lose electrons → NON-METAL
- PbBr₂: Pb at cathode, Br₂ at anode
- NaCl: Na at cathode, Cl₂ at anode
- Ions carry current inside electrolyte (not electrons)
Key Equations
- Pb²⁺ + 2e⁻ → Pb (cathode — reduction of lead bromide)
- 2Br⁻ → Br₂ + 2e⁻ (anode — oxidation of lead bromide)
- Na⁺ + e⁻ → Na (cathode — reduction of sodium chloride)
- 2Cl⁻ → Cl₂ + 2e⁻ (anode — oxidation of sodium chloride)
Common Mistakes
- Saying solid ionic compounds conduct: Ions are fixed in the lattice when solid — only molten or dissolved ionic compounds allow ions to move and carry charge
- Getting electrode products reversed: OARC — Oxidation at Anode (non-metal), Reduction at Cathode (metal) — never swap these
- Saying electrons flow through the electrolyte: Electrons flow through the external circuit (wires); inside the electrolyte, ions carry the current by moving toward electrodes
- Forgetting to balance half-equations for charge: 2Br⁻ → Br₂ + 2e⁻ — the 2 electrons balance the 2 negative charges lost from bromide ions
Practice questions for Electrolysis of Molten Compounds
Which condition is required for electrolysis to occur with an ionic compound?
State the products formed at each electrode when molten lead bromide (PbBr₂) is electrolysed.
Quick recall flashcards
How do you remember that cations go to the cathode?
CATions → CAThode (both start with CAT)
ANions → ANode (both start with AN)
Metal at the Minus (cathode is negative), Non-metal at the Plus (anode is positive).
Why does solid lead bromide NOT conduct electricity?
In the solid state, all ions (Pb²⁺ and Br⁻) are held in fixed positions in the ionic lattice by strong electrostatic forces. They cannot move, so they cannot carry electrical charge.