Trap 1: Calcination Applied to Sulphide Ores

Wrong thinking: "Both calcination and roasting heat the ore → both could apply to ZnS" Correct: ZnS is a sulphide → ROASTING (excess air). Calcination is for carbonate/hydrated ONLY. Trigger word in question: "sulphide ore" → immediately think ROASTING.

Trap 2: CO2 Line on Ellingham — "Slopes Down Like CO"

Wrong thinking: "Carbon + O2 always gives downward slope." Correct: C + O2 → CO2 has horizontal slope ($\Delta S$ ≈ 0). Only 2C + O2 → 2CO slopes downward. Trigger: The question will mention which specific reaction — read carefully.

Trap 3: Cathode vs Anode in Hall-Heroult

Wrong thinking: "Carbon electrode = anode usually in electrolysis, so Al forms at anode." Correct: $Al^{3+}$ is reduced at cathode (carbon-lined steel cell). Carbon anodes are the carbon blocks that get oxidized and consumed.

Trap 4: Cryolite as a Product vs Reagent

Wrong thinking: "Cryolite is the slag/product in Hall-Heroult." Correct: Cryolite (Na3AlF6) is the solvent/electrolyte — it is an INPUT that is NOT consumed (recycled). The PRODUCT is pure Al metal.

Trap 5: Anode Mud — Electropositive Confusion

Wrong thinking: "More electropositive metals fall as anode mud because they dissolve more." Correct: LESS electropositive (more noble) metals — Au, Ag — fall as anode mud because they RESIST oxidation. More electropositive metals (Zn, Fe) dissolve into solution.

Trap 6: Van Arkel vs Mond Temperatures

Wrong thinking: Mixing up the two processes and their temperatures. Memory device: Mond = "mild" temperatures (330–470 K = 60–200°C); Van Arkel = "extreme" temperatures (870–1700 K = 600–1430°C).