Which method of purification is represented by the following equation?
$Ti (s) + 2I_2 (g)\overset{523K}{\longrightarrow}Ti\, I_4 (g)\overset{1700K}{\longrightarrow}Ti (s) + 2I_2 (g)$
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Van Arkel Method.
The given reaction is
\(\text{Ti(s)} + 2I_2(g) \xrightarrow{523 \, \text{K}} \text{TiI}_4(g) \xrightarrow{1700 \, \text{K}} \text{Ti(s)} + 2I_2(g)\)
It is an example of the Van Arkel Method of purification. This method is used for purifying metals like titanium (Ti) and zirconium (Zr) by converting the impure metal into a volatile compound (like titanium tetraiodide, \(TiI_4\)) at a lower temperature (523 K), and then decomposing it back to pure metal at a higher temperature (1700 K).
Key Steps in the Van Arkel Method:
Formation of volatile compound: The impure metal (titanium) reacts with iodine (\(I_2\)) to form a volatile compound (\(TiI_4\)) at a moderate temperature (523 K).
Decomposition of volatile compound: The volatile compound (\(TiI_4\)) is then decomposed at a higher temperature (1700 K) to give back pure titanium and iodine gas, which is recycled.
Why it's the Van Arkel Method:
This method relies on the formation of a volatile compound and its subsequent decomposition to produce high-purity metal, which is the hallmark of the Van Arkel method.
Other Methods:
Zone Refining: This is used for purification of semiconductors and metals by melting a small region and moving it along the metal, concentrating impurities at one end.
Cupellation: Used for refining precious metals like silver, involving heating in a furnace to oxidize and remove impurities.
Poling: A process used to purify copper, where air is blown over molten copper to remove impurities.
Thus, the reaction given matches the Van Arkel Method.