The Blackened Thali

The story

Aaji's silver thali turned black overnight, just after it was used for aarti. Riya thought that the thali just got dusty and needed wiping. Chintu guessed maybe Aaji had dropped jamun on it. Kabir suggested it was the strong camphor from the aarti. Aaji, however, pointed out the window. Riya smelled the air and noticed a slightly rotten odour. With this clue, it became clear that silver reacts with sulfur gases in the air. This process forms a black layer known as silver sulfide. It's a type of corrosion described in Class 10, Metals and Non-Metals. But could the air itself really attack silver like this?

The science

When silver comes into contact with sulfur gases present in air, it reacts to form a black coating called silver sulfide. This is an example of corrosion, where the metal undergoes a chemical reaction with substances in its environment. The sulfur gases can come from decaying food, pollution, or even human skin oils, but not from camphor. So, even if you never touch a silver thali, exposure to air will slowly cause it to turn black because of this reaction.

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