IIT-JEE 2008 · Paper 1 · Chemistry Q50

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ChemistrySingle correct+3 / -1Question 50 of 69

Native silver metal forms a water soluble complex with a dilute aqueous solution of NaCN in the presence of

nitrogen

oxygen

carbon dioxide

argon

Answer and worked solution

Official answer: B

Cyanide leaching of silver (and gold) needs an oxidant, which is air (oxygen):
$\ce{4Ag + 8CN- + O2 + 2H2O -> 4[Ag(CN)2]- + 4OH-}.$
Nitrogen, carbon dioxide and argon cannot oxidise the metal.

(B)

Topics:Extraction of specific metals

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IIT-JEE 2008 · Paper 1, Chemistry question 50