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
In the van Arkel method the crude metal is heated with iodine in an evacuated vessel. The metal iodide, being covalent, volatilises at about 523 K. It is then decomposed on an electrically heated tungsten filament: the pure metal deposits on the filament and iodine is set free.
\( \displaystyle \ce{Ti(impure) + 2I2} \xrightarrow{\text{523 K}} \ce{TiI4(g)} \)
\( \displaystyle \ce{TiI4(g)} \xrightarrow{\text{1700 K}} \ce{Ti(pure) + 2I2} \)
It is a vapour phase refining method and removes oxygen and nitrogen impurities from metals such as Ti and Zr.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
van Arkel Method for Refining Zirconium or Titanium – “This method is very useful for removing all the oxygen and nitrogen present in the form of impurity in certain metals like Zr and Ti. The crude metal is heated in an evacuated vessel with iodine. The metal iodide being more covalent, volatilises:
\( \displaystyle \ce{Zr + 2I2 -> ZrI4} \)
The metal iodide is decomposed on a tungsten filament, electrically heated to about 1800K. The pure metal is thus deposited on the filament.”