Answer: Form volatile iodides at moderate temperature that decompose at higher temperature (e.g., Ti, Zr, Hf, Nb, Ta, V, B, Si).
- A Form volatile iodides at moderate temperature that decompose at higher temperature (e.g., Ti, Zr, Hf, Nb, Ta, V, B, Si)
- B Highly most metal found anywhere on the entire periodic table without any exception in standard practice under most conditions encountered
- C Any transition metal whatsoever, largely regardless of whether its halide is volatile or not as frequently observed in practice
- D Metals that generally happen to possess an unusually low melting point compared to other metals in many documented cases
Correct answer: A. Form volatile iodides at moderate temperature that decompose at higher temperature (e.g., Ti, Zr, Hf, Nb, Ta, V, B, Si)
Explanation: The Van Arkel process requires: (1) impure metal reacts with I<sub>2</sub> to form volatile MI4/MI3; (2) the iodide must decompose at higher temperature to deposit pure metal. Ti, Zr, and similar reactive metals meet this criteria.
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.