Question

The products formed when silver sulphide is shaken with $NaCN$ solution are:
A.$Na\left[ {Ag{{\left( {CN} \right)}_2}} \right]$
B.$N{a_2}\left[ {Ag{{\left( {CN} \right)}_4}} \right]$
C.$N{a_2}S$
D.$N{a_2}{S_5}$

Answer 1

Hint: To answer this question, you must recall the cyanide process used for the extraction of silver. Silver forms a complex with sodium cyanide which is water soluble.

Complete step by step solution:
This reaction is used in the Mac- Arthurs Forest process for the extraction of gold and silver from their sulphide ores by dissolving them in a solution of sodium cyanide. The three main steps involved in the extraction of silver are:
First, the ore is powdered to increase its solubility. But if the impurities contain elements like Sulphur, then the ore is dissolved in sodium cyanide solution to make it water soluble. The powdered form of the ore is now soluble in aqueous solution. This process is known as leaching of the ore.
Due to leaching, the ores become soluble in solution and can now pass through filter paper leaving behind the insoluble impurities.
The reaction can be given as
$A{g_2}S + 4NaCN \to 2Na\left[ {Ag{{\left( {CN} \right)}_2}} \right] + N{a_2}S$
The products formed are $Na\left[ {Ag{{\left( {CN} \right)}_2}} \right]$ and $N{a_2}S$.

Thus, the correct options are A and C.

Additional Information: After leaching, the solution is treated with zinc for the process of extraction. The final step involves the cementation in which a zinc electrode is immersed in the solution containing the silver cyanide resulting into the formation of zinc cyanide and pure silver metal

Note:
The leaching process can be carried out only if the ore is soluble in a particular solution and impurities should be insoluble in the same solution. The cyanide complexes formed during these reactions must be recycled or destroyed as they can be harmful.