Why can $\ce{H2S}$ be reduced by $\ce{Ag}$ when left in air: $$\ce{2 Ag + H2S -> Ag2S + H2}$$ If silver is a noble metal that should not reduce hydrogen?
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1$\begingroup$ Hydrogen sulfide won't tarnish gold or platinum but it will tarnish silver. $\endgroup$– MaxWJul 22, 2018 at 19:03
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2 Answers
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Check the electronegativity of hydrogen, silver and noble metals. In addition, though, consider that the product, $\ce{Ag2S}$, is a solid. The reaction is driven in one direction by precipitation, continually removing sulfur from the air.
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I believe silver is oxidized by oxygen to form $\ce{Ag2S}$, not displacing hydrogen from $\ce{H2S}$. $$\ce{2Ag + 1/2 O2 + H2S -> Ag2S + H2O}$$
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1$\begingroup$ Well, if silver can form hydrogen during dissolving in a cyanide solution ( gold needs oxygen, silver does not ), it could as well form hydrogen from $\ce{H2S}$. Just thought. $$\ce{2 Ag + 4 CN- + 2 H2O -> H2 + 2 [Ag(CN)2]- + 2 OH-}$$ $\endgroup$– PoutnikAug 18, 2019 at 8:36