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AFMC AFMC Solved Paper-2010

  • question_answer
    In the equation;\[4M+8C{{N}^{-}}+2{{H}_{2}}O+{{O}_{2}}\xrightarrow[{}]{{}}\] \[4{{[M{{(CN)}_{2}}]}^{-}}+4O{{H}^{-}}\] Identify the metal M.

    A)  copper                                

    B)  iron

    C)  gold                                     

    D)  zinc

    Correct Answer: C

    Solution :

                     Least reactive metals like silver (Ag) and gold (Au) are obtained by cyanide process. In this process the impure metal is treated with \[\text{NaCN}\] (solution) and air is passed. Metal is converted into soluble complex as \[4Au+8C{{N}^{-}}+2{{H}_{2}}O+{{O}_{2}}\]\[\xrightarrow[{}]{{}}\underset{(soluble)}{\mathop{4{{[Au{{(CN)}_{2}}]}^{-}}}}\,+4O{{H}^{-}}\] From this soluble complex, metal is displaced by using more electropositive metal like Zn. \[{{[Au{{(CN)}_{2}}]}^{-}}+Zn\xrightarrow[{}]{{}}\underset{(soluble)}{\mathop{{{[Zn{{(CN)}_{4}}]}^{2-}}}}\,+\underset{ppt}{\mathop{2Ag}}\,\downarrow \]


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