TBR Gen Chem Electrochem

[velokev]

TBR GChem II pg 296 #94

Answer: D
I am having difficulties understanding why B is incorrect. TBR says "If choice B were true, then tarnish could never occur, because the reduction of silver would be carried out by the sulfide anion it binds."

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[Teleologist]

I am having difficulties understanding why B is incorrect. TBR says "If choice B were true, then tarnish could never occur, because the reduction of silver would be carried out by the sulfide anion it binds."

In B the sodium hydrogen carbonate isn't participating in the exchange of electrons. It appears that silver is reduced while sulfur is oxidized. However we know this to be incorrect because otherwise why would Ag2S be stable?

In D, however, there is a clear exchange of electrons between the silver bound up in silver sulfide and elemental aluminium. Specifically, the aluminium is oxidized while the silver is reduced back to elemental silver.