Question

The cyanide complex of silver formed in the silver extraction in Mac-Arthurs Forrest cyanide process is:
A. ${{\left( \text{Ag(CN}{{\text{)}}_{2}} \right)}^{-}}$
B. ${{\text{K}}_{2}}\left( \text{Ag(CN}{{\text{)}}_{3}} \right)$
C. ${{\left( \text{Ag(CN}{{\text{)}}_{4}} \right)}^{2-}}$
D. $\text{N}{{\text{a}}_{3}}\left( \text{Ag(CN}{{\text{)}}_{4}} \right)$

Answer 1

Hint: For this problem, we have to study the complete process of the formation of the cyanide complex of silver which is formed during the extraction of silver. By writing all the reactions we can find the product.

Complete Step-by-Step answer:
- In the given question, we have to choose the correct cyanide complex of silver formed during the silver extraction.
- Mac-Arthurs Forest process is a process that is used to extract the gold and silver from the ores by dissolving them in a solution of cyanide.
- For the extraction of the silver, three steps are followed that are:
1. Firstly, the ore is converted into powdered form. But if the impurities of elements like sulphur are present then it is dissolved in the sodium cyanide solution to make it soluble.
2. Now, the powdered form of the ore can dissolve and the process is known as leaching. Due to leaching the silver or gold become soluble in the solution and can pass through the filter paper whereas other impurities cannot pass.
3. Now, the solution formed is treated with zinc or carbon for the extraction purpose. The final step includes the cementation in which the zinc electrode is immersed in the solution of containing gold cyanide and carbon paste.
- The balanced chemical reaction will be:
$\text{A}{{\text{g}}_{2}}\text{S + }\text{2C}{{\text{N}}^{-}}\text{ + }{{\text{O}}_{2}}\to \text{ 2}{{\left( \text{Ag(CN}{{\text{)}}_{2}} \right)}^{-}}\ \text{+ S}{{\text{O}}_{2}}$
$\text{Zn + 2}{{\left( \text{Ag(CN}{{\text{)}}_{2}} \right)}^{-}}\to \text{ }{{\left( \text{Zn(CN}{{\text{)}}_{4}} \right)}^{2-}}\ \text{+ 2Ag}$
Therefore, option A is the correct answer.

Note: Gold is also extracted using the Macarthur Forrest cyanide process as it is present in low concentration so it should be separated from other impurities. In the above process the oxygen acts as a reducing agent.