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Consider the following metallurgical processes
$(i)$ Heating impure metal with $CO$ and distilling the resulting volatile carbonyl (boiling point $43\,^oC$) and finally decomposing at $150\,^oC$ to $200\,^oC$ to get the pure metal.
$(ii)$ Heating the sulphide ore in air until a part is converted to oxide and then further heating in the absence of air to let the oxide react with unchanged sulphide.
$(iii)$ Electrolysing the molten electrolyte containing approximately equal amounts of the metal chloride and $CaCl_2$ to obtain the metal.
The process used for obtaining sodium, nickel and copper are, respectively,
$(i),\, (ii)$ and $(iii)$
$(ii),\, (iii)$ and $(i)$
$(iii), \,(i)$ and $(ii)$
$(ii),\, (i)$ and $(iii)$
Solution
Electrolyzing the molten electrolyte $( NaCl )$ containing $CaCl _2$ to obtain sodium metal in Down's method. The mixture $CaCl _2+ KF$ lowers the melting point of $NaCl$ from $800^{\circ} C$ to $600^{\circ} C$. Sodium is obtained at the cathode which is an iron rod. The anode is graphite rod.
Heating impure metal with $CO$ and distilling the resulting volatile carbonyl (b.pt. $43^{\circ} C$ ) and finally decomposing at $150^{\circ} C$ to $230^{\circ} C$ to get the pure nickel metal.
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 sulphide to form copper metal.
$2 Cu _2 S +3 O _2 \rightarrow 2 Cu _2 O +2 SO _2$
$2 Cu _2 O + Cu _2 S \rightarrow 6 Cu + SO _2$
This is an example of auto reduction and the process is called Bessemerization.
The processes used for obtaining sodium, nickel and copper are $3,1$ and $2$ respectively.
