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JEE Main202225 Jun 2022Morning ShiftChemistryGeneral Principles and Processes of Isolation of MetalsActual

Leaching of gold with dilute aqueous solution of NaCN in presence of oxygen gives complex A , which on reaction with zinc forms the elemental gold and another complex B . A and B , respectively are

Options

  1. AAu CN 2 - and Zn CN 4 2 -
  2. BAu CN 4 - and Zn CN 2 OH 2 2 -
  3. CAu CN 2 - and Zn OH 4 2 -
  4. DAu CN 4 2 - and Zn CN 6 4 -

Correct answer

A. Au CN 2 - and Zn CN 4 2 -

Step-by-step solution

Extraction of gold is carried out by leaching process. Sodium cyanide ( NaCN ) has been used as leaching reagent for gold. Metal is converted into the soluble cyanide complex on reaction with sodium cyanide. 4 Au  + 8 CN - + 2 H 2 O + O 2   →   4 [ Au ( CN ) 2 ] - X + 4 OH - Silver is later recovered by displacement with Zn . 2 Au CN 2 -   +   Zn   → Displacement Zn CN 4 2 - Y   +   2 Au X   and   Y are [ Au ( CN ) 2 ] - and  [ Zn ( CN ) 4 ] 2-

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