Answer: Calcium silicate (CaSiO3) formed from CaO + SiO 2.
- A Calcium silicate (CaSiO3) formed from CaO + SiO<sub>2</sub>
- B Pure unreacted silica left over from the original ore
- C Iron carbide formed from excess carbon reacting with iron
- D Carbon dioxide gas trapped within the molten iron
Correct answer: A. Calcium silicate (CaSiO3) formed from CaO + SiO<sub>2</sub>
Explanation: Limestone (CaCO<sub>3</sub>) decomposes to CaO + CO<sub>2</sub>; CaO + SiO<sub>2</sub> (gangue) → CaSiO3 (slag), which floats on molten iron.
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.