Question

(a) Which solution is used for the leaching of silver metal in the presence of air in the metallurgy of silver?
(b) Out of ‘${\text{C}}$’ and ‘${\text{CO}}$’, which is a better reducing agent at the lower temperature range in the blast furnace to extract iron from the oxide ore?

Answer 1

Hint: The process in which the valuable metals are converted to their soluble salts and the impurities remain insoluble is known as leaching. The thermodynamic factor decides the better reducing agent.

Complete step by step answer:
(a) The roasted ore of silver is leached using a solution of sodium cyanide in the presence of air. The process in which the valuable metals are converted to their soluble salts and the impurities remain insoluble is known as leaching. The leaching process of silver metal by sodium cyanide is carried out in the presence of oxygen in air.
The role of sodium cyanide in this process of leaching is to dissolve the silver metal to form a silver cyanide complex. The reaction is as follows:
${\text{4Ag + 8NaCN + 2}}{{\text{H}}_2}{\text{O + }}{{\text{O}}_2}{\text{ }} \to {\text{ 4Na}}\left[ {{\text{Ag}}{{\left( {{\text{CN}}} \right)}_2}} \right]{\text{ + 4NaOH}}$
The pure silver metal can be obtained from the silver cyanide complex by a displacement reaction with zinc metal. The reaction is as follows:
${\text{2Na}}\left[ {{\text{Ag}}{{\left( {{\text{CN}}} \right)}_2}} \right]{\text{ + Zn }} \to {\text{ N}}{{\text{a}}_2}\left[ {{\text{Zn}}{{\left( {{\text{CN}}} \right)}_4}} \right]{\text{ + 2Ag}}$
Thus, the solution used for the leaching of silver metal in the presence of air in the metallurgy of silver is sodium cyanide $\left( {{\text{NaCN}}} \right)$. Potassium cyanide $\left( {{\text{KCN}}} \right)$ can also be used.
(b) During the extraction of iron from the oxide ore, the oxide of iron $\left( {{\text{FeO}}} \right)$ gets reduced to iron $\left( {{\text{Fe}}} \right)$ and ${\text{C}}$ or ${\text{CO}}$ gets oxidised to ${\text{C}}{{\text{O}}_2}$.
The value of \[{G^{\text{o}}}\] for the change of ${\text{C}}$ to ${\text{C}}{{\text{O}}_2}$ is less than the value of \[{G^{\text{o}}}\] for the change of ${\text{CO}}$ to ${\text{C}}{{\text{O}}_2}$.
Due to this, ${\text{C}}$ is a better reducing agent than ${\text{CO}}$ at the lower temperature range in the blast furnace to extract iron from the oxide ore.

Note: The most common ore of silver is argentite or silver glance and that of copper is copper matte. When the value of \[{G^{\text{o}}}\] is smaller the reducing agent is better at a lower temperature range.