Question

Mac Arthur process is used for the extraction of:
(A) Au
(B) Pt
(C) Cu
(D) Zn

Answer 1

Hint: Two metals are extracted using this process. They are valuable rare metals.

Complete step-by-step answer:
Let us take our time to understand the Mac Arthur process first.
Extraction of metals is done by carrying out a series of steps. At each stage the metal is gradually more of itself than the impurities it once surrounded itself with. The first process in this series is known as “concentration of ores”. The impurities are known as “gangue” and are removed by a variety of methods which greatly depend on the type of ore, the place where it is found and the cost of its overall production.
In case of metals like gold and silver, a process called leaching is used to concentrate the metals.We have the Mac Arthur process which is a leaching method to extract gold and silver, where a cyanide solution is used. It is a dilute sodium cyanide solution ($NaCN$) for silver and dilute potassium cyanide solution ($KCN$) for gold. The metals are leached away in the form of coordinate compounds in the presence of oxygen. Later the metals are obtained by a simple displacement reaction using zinc metal. The equations of the above processes are as below:
Leaching of the metal
\[4M(s)+8C{{N}^{-}}(aq)+2{{H}_{2}}O(aq)+{{O}_{2}}(g)\to 4{{[M{{(CN)}_{2}}]}^{-}}(aq)+4O{{H}^{-}}\]
Here “M” is gold or silver.
- Getting pure metal through displacement reaction with zinc
\[2{{[M{{(CN)}_{2}}]}^{-}}(aq)+Zn(s)\to {{[Zn{{(CN)}_{4}}]}^{2-}}(aq)+2M(s)\]

Therefore the answer to the above question is option (A) Au or gold.

Note:
The leaching process is only carried out when the ore is soluble in a particular solution and not the substances that make it impure. Many times some other substance is also able to dissolve in the leaching solution along with the ore but this is later separated.
The displacement reaction carried out in the above processes is only possible because zinc has a higher tendency to oxidise than gold or silver and therefore zinc acts as a reducing agent.