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19. Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.

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    Answered by

    alok kumar singh | Contributor-Level 10

    4 months ago

    19. The metal gold is a nonreactive metal. It is found as a native metal in its free state.

    So, it is not compulsory to separate it by a chemical process. Thus, gold is leached to get it in its pure form. In the metallurgy of gold (Au), the respective metal is leached with a dilute mixture of NaCN or KCN in the presence of air where Gold (Au) is oxidized by oxygen of the air to Au+cation which then merges with ions to form a soluble compound.

    4Au (s)+8CN− (aq)+O2− (g)+2H2O− (aq)→4 [Au (CN)2]− (aq)+4OH− (aq)

    Gold is then obtained from this soluble compound x by replacement method by using a much

    ...more

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Statement I: Leaching of gold with cyanide ion in absence of air / O2 leads to cyano complex of Au(III)

Statement II: Zinc is oxidized during the displacement reaction carried out for gold extraction.

In the light of the above statements, choose the correct answer form the options given below.
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Leaching involves the given reaction,

4 A u ( s ) + 8 C N − ( a q ) + 2 H 2 O ( a q ) + O 2 ( g ) → 4 [ A u ( C N ) 2 ] − ( a q ) + 4 O H − ( a q )              

Here, O2 is required for formation of Au (l) cyanide complex but no complex in absence of O2.

2 [ A u ( C N ) 2 ] − ( a q ) + Z n ( s ) → [ Z n ( C N ) 4 ] 2 − ( a q ) + 2 A u ( s )                

In above displacement reaction, Zn is oxidized.

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