JEE Main 2022 — General Principles and Processes of Isolation of Metals Question with Solution

i) Copper was smelted in an open furnace. The slightly impure copper had impurities, mostly sulphur dioxide which bubbled up through the copper as it solidified. That gave a blistered surface and the results of the smelting were called blister copper. Copper is purified by electrolytic refining of blister copper.

ii) The principle of froth floatation is that sulphide ores are preferentially wetted by pine oil, whereas the gangue particles are wetted by water. Collectors are added to enhance the non-wettability of the mineral particles. Examples of collectors are pine oil, fatty acids and xanthates.

iii) In the metallurgy of gold, the respective gold ore is leached with a dilute solution of $\mathrm{NaCN}$ or $\mathrm{KCN}$ in the presence of air (for ${\mathrm{O}}_2$) from which the gold is obtained later by replacement:

$4\mathrm{Au}\left(\mathrm{s}\right)+8{\mathrm{CN}}^{-}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 4{\left[\mathrm{Au}{\left(\mathrm{CN}\right)}_2\right]}^{-}\left(\mathrm{aq}\right)+4{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)$

$2{\left[\mathrm{Au}{\left(\mathrm{CN}\right)}_2\right]}^{-}\left(\mathrm{aq}\right)+\mathrm{Zn}\left(\mathrm{s}\right)\to {\left[\mathrm{Zn}{\left(\mathrm{CN}\right)}_4\right]}^{2-}\left(\mathrm{aq}\right)+2\mathrm{Au}\left(\mathrm{s}\right)$