Question

\[C{{N}^{-}}\] a solution used in extraction of which metal
A. Ag
B. Ti
C. Zn
D. Sn

Answer 1

Hint: All metal is not found in a pure state but in ore (in the form of a mixture of metal and impurities) so, to extract metal from their ores many chemical processes are applicable. But in this question, we need to tell what metal is extracted by mainly cyanide solution. The mostly used cyanide solutions for extraction are sodium cyanide and potassium cyanide. The process with which cyanide extracts specific metal (need to know) is the cyanide process.

Complete Step by Step Answer:
Let us consider sodium cyanide solution for extracting metal such as NaCN. Sodium cyanide is a salt formed with a strong base and weak acid. Thus, NaCN overall is of basic character, and that basic character is due to the lone pair of electrons of nitrogen (CN act like lewis base or reducing agent).

The cyanide process Is the process of extraction of gold and silver mostly from their ore. In this method, metal ore (silver ore or gold ore) is made to dissolve in a dilute solute of alkaline cyanide (sodium cyanide). After this, a liquid complex of silver or gold will be formed which is soluble in water such as
\[A{{g}_{2}}\text{S }+\text{ 4}NaCN\to \text{ 2}Na\left[ Ag{{\left( CN \right)}_{2}} \right]+N{{a}_{2}}S\]

The formation of the bond between cyanide and silver is possible because of the lone pair of nitrogen. Nitrogen donates its lone pair to silver resulting in the formation of a coordinate bond. But still pure silver is not extracted. So for this, we add zinc to this complex soluble solution. Zinc which is more electropositive (less electronegative) than silver displaces it from the solution such as
\[2Na\left[ Ag{{\left( CN \right)}_{2}} \right]\text{ }+\text{ }Zn\text{ }\to \text{ }N{{a}_{2}}\left[ Zn{{\left( CN \right)}_{4}} \right]\text{ }+\text{ 2}Ag\]
Thus, Zinc is used to help in the extraction of pure silver, and the cyanide process helps to extract mostly silver and gold.
Thus, the correct option is A.

Note: Why cyanide can't extract zinc (extracted by zinc blend)? Because zinc is a more electropositive metal (tendency to give electrons or can say good reducing agent) and on other hand, cyanide is also a reducing agent due to the lone pair of electrons of nitrogen. Because of this cyanide method is not a good practice to extract zinc. To get extracted by the cyanide method, metal should be less electropositive, more electronegative, oxidizing agent, and electron-deficient to form a bond against the reducing agent (cyanide).