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Question

Which of the following metal is leached by the cyanide process?


A

Al

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B

Ag

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C

Cu

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D

Na

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Solution

The correct option is B

Ag


The explanation for correct option (B) Ag

Leaching by cyanide process:

  • Leaching is a process that is used widely in metallurgy where the treatment of ores takes place with chemicals to convert the valuable metals while the impurities remain insoluble.
  • The metals such as gold and silver can be leached with a dilute solution of sodium cyanide or potassium cyanide in the presence of air.
  • The chemical reaction can be depicted as:

Ag(s)+2CN(aq)+2H2O(l)+O2(g)[Ag(CN)2](aq)+4OH(aq)

  • The silver complex formed with cyanide is a water-soluble complex.
  • Further reduction takes place in presence of Zinc with the cyanide complex. The chemical reaction can be depicted as:

[Ag(CN)2](aq)+2Zn(s)2[Zn(CN)4]2-(aq)+Ag(s)

  • The complex formed between the zinc and cyanide is also a water-soluble complex

Explanation for incorrect options:

Metals such as Aluminum, Copper, and Sodium cannot be leached by the cyanide process. Thus options B, C, and D stand incorrect.

Hence, the correct option is A i.e. Ag.


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