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?

September 15, 2024

Answer

The blackness of silver coin is due to the formation of silver sulphide in its surface due to its exposure to air. On boiling, the aluminium foil reacts with the layer of silver sulphide and displaces silver from silver sulphide to from aluminium sulphide and silver. This makes the coin shiny.

3𝐴𝑔²𝑆 + 2𝐴𝑙 → 6𝐴𝑔 + 𝐴𝑙₂𝑆₃

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