Answer: Carbon monoxide (from coke): ZnO + CO → Zn + CO 2.
- A Carbon monoxide (from coke): ZnO + CO → Zn + CO<sub>2</sub>
- B Hydrogen gas injected directly into the roasting furnace
- C Molten aluminium added as the reducing agent for zinc oxide
- D Calcium metal added as the reducing agent for zinc oxide
Correct answer: A. Carbon monoxide (from coke): ZnO + CO → Zn + CO<sub>2</sub>
Explanation: ZnO + C → Zn + CO (at ~1000°C); Zn vapour is condensed. The reaction produces Zn vapour because Zn's boiling point (907°C) is below the reaction temperature.
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.