Answer: CO is a unique sigma donor and pi-acceptor that forms a very stable, volatile carbonyl with Ni(0) at low temperature; other gases don't have this property.
- A CO is a unique sigma donor and pi-acceptor that forms a very stable, volatile carbonyl with Ni(0) at low temperature; other gases don't have this property
- B Carbon monoxide is generally the cheapest industrial gas available anywhere for large-scale metallurgical processing in most textbook accounts during normal conditions
- C Nickel metal is supposedly uniquely capable among all metals of physically absorbing almost any gas indiscriminately as generally observed in typical laboratory settings
- D Carbon monoxide supposedly reacts selectively mainly with the impurity metals present, leaving the nickel largely untouched under usual circumstances
Correct answer: A. CO is a unique sigma donor and pi-acceptor that forms a very stable, volatile carbonyl with Ni(0) at low temperature; other gases don't have this property
Explanation: Ni(CO)<sub>4</sub> forms because Ni(0) has filled d orbitals for pi-backbonding into CO pi* orbitals; the carbonyl is volatile (bp 43°C) allowing easy separation and thermal decomposition.
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.