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Which method of purification is represented by the following equation?
$Ti(s) + 2I2(g)\xrightarrow{{523K}}Ti{I_4}(g)\xrightarrow{{1700K}}Ti(S) + 2{I_2}(g)$
A: Zone refining
B: Cupellation
C: Polling
D: Van Arkel

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Last updated date: 20th Jun 2024
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Answer
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Hint: In metallurgy, the process of refining involves the purification of an impure metal. Refining process differs from other processes like calcining or smelting which generally include a chemical change in the raw material. On the other hand, in the refining process, the final product is chemically identical to the raw material i.e. original one (only it is its purest form).

Complete step by step answer:
Method of Zone refining (option A) is also known as zone melting. In this technique, a circular form of mobile heater is usually fixed at one corner of a rod made from impure metal. This technique is utilised in the case where impurities dissolve in molten state in comparison to that in solid form of the metal. Silicon and germanium are generally purified by this technique.
Method of Cupellation (option B) is a technique to recover the precious metals from impurities (like lead, tin, copper, etc) by melting impure metal (alloy) in a cup and then impurities are oxidized at high temperature through hot air blast. Silver and gold are generally purified by this technique.
Poling (option C) is a technique which is employed to recover or purify metals which possess oxidized impurities. For example, it is specifically used to recover/purify metals such as copper or tin which are present in the impure form of their oxides (copper oxide and tin oxide, respectively).
Van Arkel (option D) is a technique that involves thermal decomposition of volatile compounds such as iodide. The formation of Iodide initially takes place by directly combining the iodine with the metal that has to be purified. Then, the metallic iodide undergoes heating at high temperature to get decomposed. As a result, pure form of metal is obtained. Zirconium and Titanium are generally purified by this technique.
$Ti(s) + 2I2(g)\xrightarrow{{}}Ti{I_4}(g)$
$Ti{I_4}(g)\xrightarrow{{}}Ti(S) + 2{I_2}(g)$

Thus, the correct option is (D) i.e. Van Arkel.

Note:
Van Arkel technique is also called the crystal bar process, vapour phase refining or iodide process. This was the first technique to produce pure form of ductile metallic zirconium at commercial level.