Silver is plated onto a metal object by immersing the object in an aqueous solution…
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
Silver is plated onto a metal object by immersing the object in an aqueous solution containing Ag(CN)2−(aq). In a refining process, the used plating solution is treated with powdered zinc, which reduces the silver complex ion to metallic silver while the zinc is oxidized.
The two relevant half-reactions occurring in the mixture are:
Ag(CN)2−(aq)+e−→Ag(s)+2CN−(aq)Zn(s)→Zn(CN)42−(aq)+2e−
(a) Combine the two half-reactions to obtain the balanced overall equation that describes the chemical change occurring in the refining vessel.
(b) Determine the total number of moles of electrons transferred when 1.00 mol of Zn reacts completely under these conditions.
(c) A batch process starts with 5.60 g of powdered zinc and an excess of Ag(CN)2− solution. Calculate the theoretical mass of pure silver that can be recovered.
(d) In an industrial run, only 91.5 % of the theoretical silver mass calculated in part (c) is actually isolated. Giving a possible particulate-level explanation, account for why the percent yield might be less than 100 %.