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(i) How will you purify metals by using ...

(i) How will you purify metals by using iodine ?
(ii) Boron does not react directly with hydrogen. Suggest one method to prepare diborane from `BF_(3)`.

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(i) This method is based on the thermal decomposition of metal compounds which lead to the formation of pure metals. Titanium and zirconium can be purified using this method. For example, the impure titanium metal is heated in an evacuated vessel with iodine at a temperature of 550 K to form the volatille titanium tetra-iodide. `(Til_(4))`. The impurities are left behind, as they do not react with iodine.
`Ti_((s))+2l_(2(s))to Til_(4)("vapour")`
The volatile titanium tetraiodide vapur is passed over a tungsten filament at a temperature around 1800 K. The titanium tetraiodide is decomposed and pure titanium is deposited on the filament. The iodine is reused.
`Til_(4)("vapour")to Ti_((s))+2I_(2(s))`
(ii) Boron does not react directly with hydrogen. However it forms a variety of hydrides called boranes. Treatment of gaseous boron trifluoride with sodium hydride around 450 K gives diborane. `underset(("Borontrifluoride"))(2BF_(3))+6NaHoverset(450" K")to underset(("Diborane"))(B_(2)H_(6))+6NaF`
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Knowledge Check

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