Question

In the cyanide process for the extraction of silver, sodium cyanide is used to:
A.Convert silver into a soluble silver complex
B.Reduce silver
C.Precipitate silver
D.Oxidise silver

Answer 1

Hint: Sodium cyanide is highly reactive towards metals, and dissolves a metal into its corresponding metal cyanide form. The soluble metal cyanide is then used to extract the pure metal from it. The same principle is also employed in extracting silver from its ore by using sodium cyanide.

Complete step by step answer:
As the name suggests, the “cyanide process for the extraction of silver” is the method of extracting silver from its ore by using cyanide such as sodium cyanide or potassium cyanide. This process of extracting silver from its ore is called the Macarthur-Forrest process of silver extraction, named after the scientists' John S. MacArthur and Robert W. Forrest who invented it.

This process mainly comprises three steps: The first step is the one in which the silver ore is finely ground into tiny particles, and then reacted with the dilute solution of sodium cyanide. The silver ore dissolves in the sodium cyanide solution and a soluble silver cyanide complex is formed. This step is called the leaching process in which the insoluble silver is extracted from its ore and changed into the soluble silver cyanide.
Now, the silver cyanide solution is treated with a zinc solution in which the silver cyanide precipitates out, and pure silver is finally obtained from its ore.

The process of silver extraction can be represented by the following reactions:
$4Ag+8{CN}^{-}+2H_{2}O+O_2\to 4{[Ag{\left(CN\right)}_2]}^{-2}+4{OH}^{-}$
$4{[Ag(CN{)}_2]}^{-}+Zn\to {[Zn(CN{)}_4]}^{2-}+2Ag$

Hence, it can be concluded that sodium cyanide is used to convert silver into a soluble silver complex in the extraction process of silver from its ore

So, the correct answer is Option A.

Note: Leaching Process:
The leaching process is used to convert an insoluble substance into a soluble one by dissolving it in a particular solvent.
Silver is readily soluble in sodium or potassium cyanide. So, they are used in the leaching of silver from its ore in the silver extraction process.

Complex:
A complex is also called a coordination compound in which there is a central metal atom or ion, surrounded by neutral or negatively charged species called ligands.
In the case of silver extraction, the complex formed is $2{[Ag(CN{)}_2]}^{-}$ , in which,${Ag}^{+}$ is the central metal ion, and ${CN}^{-}$ ions are the ligands.

Precipitation Reaction:
A precipitation reaction is a reaction in which an insoluble salt is separated from a solution as a precipitate.
Silver is insoluble in zinc solution. So, it precipitates out when silver cyanide is reacted with a zinc solution.