Cryolite's Role in Aluminum Electrolysis

Steps:

• Identify the Hall-Héroult process: electrolysis of Al2O3 dissolved in molten cryolite (Na3AlF6) to produce aluminum.
• Note cryolite lowers the melting point from 2050°C to ~950°C and increases electrolyte conductivity.
• Evaluate anode reactions: carbon anodes oxidize to CO2, requiring replacement; cathodes do not.
• Assess cryolite's function: it dissolves Al2O3, providing Al3+ ions for electrolysis without reacting with impurities.

Why A is correct:

• Cryolite dissolves Al2O3, increasing the concentration and mobility of Al3+ ions in the electrolyte, enabling efficient electrolysis (per Faraday's laws of electrolysis).

Why the others are wrong:

• B: Cryolite acts as a solvent, not a reactant for impurities; slag forms from fluxing agents like CaF2.
• C: Carbon cathodes do not react significantly with oxygen; they are stable and long-lasting.
• D: While anodes react with oxygen, this describes the anode, not cathode replacement.

Final answer: A