Answer: Purify bauxite to alumina (Al 2 O 3 ) before electrolysis.
- A Purify bauxite to alumina (Al<sub>2</sub>O<sub>3</sub>) before electrolysis
- B Extract iron from its oxide ore in a blast furnace
- C Electrolytically refine impure blister copper
- D Produce steel from pig iron in a converter
Correct answer: A. Purify bauxite to alumina (Al<sub>2</sub>O<sub>3</sub>) before electrolysis
Explanation: Bayer process: bauxite + NaOH → NaAlO2 (sodium aluminate); filtered then precipitated to give pure Al(OH)<sub>3</sub> → Al<sub>2</sub>O<sub>3</sub> by calcination.
An Ellingham diagram plots ΔG° of oxide formation against temperature for different metals; whichever line is LOWER (more negative ΔG°) at a given temperature reduces the oxide of any metal whose line sits above it - the basis of carbon reduction (Fe, Zn) vs electrolytic reduction (Al, Mg, Na) decisions.
Concept context
The science of extracting metals from ores and refining them for use. Covers concentration methods, reduction techniques, refining processes, and the thermodynamic principles that govern metal extraction.