Answer: Extracting gold (4Au + 8NaCN + O 2 + 2H 2 O → 4Na[Au(CN)2] + 4NaOH).
- A Extracting gold (4Au + 8NaCN + O<sub>2</sub> + 2H<sub>2</sub>O → 4Na[Au(CN)2] + 4NaOH)
- B Extracting iron from its oxide ore using a blast furnace under usual circumstances
- C Electrolytically refining impure blister copper according to most researchers
- D Extracting aluminium from bauxite via electrolysis in the majority of cases studied
Correct answer: A. Extracting gold (4Au + 8NaCN + O<sub>2</sub> + 2H<sub>2</sub>O → 4Na[Au(CN)2] + 4NaOH)
Explanation: Gold dissolves in aerated dilute NaCN solution; the complex Na[Au(CN)2] is then reduced by zinc to deposit gold.
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.