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CAIE A Level Chemistry 9701 · Chemistry of transition elements

Chemistry of transition elements: explain question

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Silver(I) ions in aqueous solution form the complex ion [Ag(HX2O)X2]X+\ce{[Ag(H2O)2]+}, which is linear. When an excess of aqueous sodium cyanide is added, the complex [Ag(CN)X2]X−\ce{[Ag(CN)2]-} forms. Explain, in terms of ligand exchange, why the reaction occurs, and use the following standard electrode potentials to explain why silver(I) cyanide does not precipitate when the cyanide is added.

AgX++eX−⇌Ag\ce{Ag+ + e- <=> Ag} E∘=+0.80E^\circ = +0.80 V

[Ag(CN)X2]X−+eX−⇌Ag+2 CNX−\ce{[Ag(CN)2]- + e- <=> Ag + 2CN-} E∘=−0.31E^\circ = -0.31 V

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