Q.Give the basic requirement for vapour phase refining.

Step 1. The core requirement of vapour phase refining is that a chosen reagent must react SPECIFICALLY with the metal (not with its impurities) to form a new compound.

Step 2. This compound must be VOLATILE -- easily vaporised -- so that it physically separates from and leaves behind the solid, involatile impurities that do not form the same compound with the reagent.

Step 3. The compound must also be capable of being cleanly DECOMPOSED, typically by heating it further (often on a hot surface, as with the Van-Arkel tungsten filament), releasing the pure metal and regenerating the original reagent gas, which can then be recycled. …

State the two-part requirement (volatility for separation, decomposability for recovery) that any vapour-phase refining reagent/compound pair must satisfy, i …

• Focusing only on 'the compound must be volatile' and forgetting the equally essential second requirement -- it must ALSO be cleanly decomposable afterwards, o …