Answer: In the absence of air (or limited air).
- A In the absence of air (or limited air)
- B In a large excess of air to fully oxidise the ore
- C Together with water to dissolve the impurities
- D Together with concentrated hydrochloric acid
Correct answer: A. In the absence of air (or limited air)
Explanation: Calcination heats carbonate or hydroxide ores without air; e.g., CaCO<sub>3</sub> → CaO + CO<sub>2</sub> (limestone).
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.