Question

Consider the following isolation/purification processes.

(I) Heating impure metal with $I_2$ at $150-{200}^{\circ }C$ and passing the resulting volatile iodide on hot tungsten filament at ${1400}^{\circ }C$ to get the pure metal.
(II) Heating the sulphide ore in the air until a part is converted to oxide and then further heating in the absence of air to let the oxide react with unchanged metal sulphide to get the metal.
(III) Electrolysis of the molten electrolyte containing metal oxide and cryolite or fluorspar to obtain the metal.

The processes used for obtaining aluminium, titanium and lead are respectively :

• A. (I), (II) and (III)
• B. (II), (III) and (I)
• C. (III), (I) and (II)
• D. (II), (I) and (III)

Answer 1

Answer: (C)

(III), (I) and (II)

Aluminium (III)

Titanium (I)

Lead (II)

(I) Van-Arkel method: This method is used for ultrapure metals like Ti, Zr etc. The metal is converted into its volatile stable compound such as $Ti{I}_4$, leaving behind impurities. The stable volatile compound thus formed is decomposed to get the pure metal.

$\frac{Ti}{\left(impure\right)}+2I_2\underrightarrow{500k}Ti{I}_4\underrightarrow{1675K}Ti+\frac{2I_2}{\left(pure\right)}$

(II) $2\text{PbS}+3{\text{O}}_2\stackrel{\Delta }{⟶}2\text{PbO}+2{\text{SO}}_2$

$\text{PbS}+2\text{PbO}\underset{\text{temp}}{\overset{\text{high}}{\to }}3\text{Pb}+{\text{SO}}_2$

(III) ${\text{Cathode : Al}}^{3+}$ $\text{(melt)}+3{\text{e}}^{-}⟶\text{Al}$ (l)

$\text{Anode : C(s)}+{\text{O}}^{2-}\text{(melt)}⟶\text{CO(g)}+2{\text{e}}^{-}$
$\text{C(s)}+2{\text{O}}^{2-}\text{(melt)}⟶{\text{CO}}_2\text{(g)}+4{\text{e}}^{-}$