What is the primary reason why silver articles tarnish when exposed to air for a long duration?

Question

Examoogle · Accepted Answer

The correct answer is Option B: Reaction with sulfur compounds in the air. Silver articles tarnish when exposed to air because silver is a relatively unreactive metal that reacts with sulfur-containing gases like hydrogen sulfide ($H_{2}S$) present in the atmosphere. This reaction results in the formation of a black coating of silver sulfide ($Ag_{2}S$) on the surface of the silver.

Step-by-Step Solution & Concepts:
Silver articles tarnish when exposed to air because silver is a relatively unreactive metal that reacts with sulfur-containing gases like hydrogen sulfide ($H_{2}S$) present in the atmosphere. This reaction results in the formation of a black coating of silver sulfide ($Ag_{2}S$) on the surface of the silver.

Working Principle: The tarnishing process is a chemical corrosion reaction. Silver reacts with atmospheric hydrogen sulfide, which is often released from industrial processes or the decomposition of organic matter, to form silver sulfide. The chemical equation for this reaction is $2Ag(s) + H_{2}S(g) \rightarrow Ag_{2}S(s) + H_{2}(g)$. This creates a thin, stable film that darkens the appearance of the metal over time.

Key Formulas: $2Ag + H_{2}S \rightarrow Ag_{2}S + H_{2}$ — The formation of silver sulfide

Key Points: Silver is not highly reactive with oxygen at room temperature, which is why it does not 'rust' like iron.; The black layer formed is silver sulfide ($Ag_{2}S$).; Tarnishing can be reversed by chemical cleaning processes that reduce the sulfide back to metallic silver.

Applications: Used to identify the presence of sulfur compounds in industrial gas analysis.; Understanding preservation techniques for silver jewelry and cutlery.

Additional Info: Silver is a noble metal, meaning it is resistant to oxidation and corrosion in moist air, unlike iron or copper.. Option A is incorrect because silver does not readily react with oxygen at room temperature. Option C is incorrect because nitrogen is inert under these conditions. Option D is incorrect because moisture alone does not cause the chemical color change characteristic of tarnish.

Answer: B is correct — Silver articles react with sulfur compounds in the air to form a layer of silver sulfide.

Exam Tip: In competitive exams, remember that while iron corrodes due to oxidation (rusting), silver tarnishes specifically due to sulfidation. Do not confuse the two!

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Option A: Reaction with oxygen to form silver oxide

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Option C: Reaction with nitrogen gas

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Option D: Absorption of moisture from the atmosphere

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