Silver Tarnishing Explained

Silver articles turn black when exposed to air due to a chemical reaction with components present in the atmosphere. This process is known as tarnishing.

Identifying the Cause of Blackening

The black layer formed on silver is primarily silver sulfide ($Ag₂S$). This compound results from the reaction of silver ($Ag$) with hydrogen sulfide ($H₂S$) gas.

The relevant chemical reaction is:

$2Ag(s) + H₂S(g) → Ag₂S(s) + H₂(g)$

Role of Sulphur in Air

Hydrogen sulfide ($H₂S$) is a gas containing sulphur, which is found in trace amounts in the air. While other gases like chlorine, carbon dioxide, and nitrogen are also present in the air, they do not cause silver to turn black in this manner.

• Chlorine: Highly reactive but doesn't form the black sulfide layer.
• Carbon: Can deposit as soot but doesn't chemically react to cause blackening.
• Sulphur: Present as $H₂S$ in the air, directly reacting with silver to form black $Ag₂S$.
• Nitrogen: Largely inert and does not react with silver.

Therefore, the presence of sulphur compounds, specifically hydrogen sulfide, in the air is responsible for the blackening of silver articles.

Conclusion

Based on the chemical reactivity, Sulphur is the element whose compounds in the air cause silver articles to turn black.