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Question

Samuel had a Silver coin which turned black. He kept coin in a bowl lined with aluminium foil. Then he filled the bowl with water and boiled it. After sometime, he found that the coin has become new. Its blackness disappeared. How did it happen?

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Answer

Samuel’s silver coin turned black due to the formation of silver sulfide (Ag₂S), which occurs when silver reacts with sulfur compounds in the air. This process is called tarnishing.

How did the blackness disappear?

Samuel placed the coin in a bowl lined with aluminum foil, added water, and boiled it. This setup created a redox reaction between silver sulfide (Ag₂S) and aluminum (Al).

Chemical Reaction:

3Ag2S + 2Al → 6Ag + Al2S3

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