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Question:

What happens when silver is leached with NaCN in the presence of air?

Solution:

When silver is leached with NaCN in presence of air, Ag is oxidised to Ag+ and forms a complex sodium argentocyanide ([Ag(CN)₂]⁻) from which the silver is obtained later by replacement. 4Ag + 8NaCN + 2H₂O + O₂ → 4Na[Ag(CN)₂] + 4NaOH