A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining. Name the black substance formed and give its chemical formula:

Silver Sulphide (Ag₂S)

Explanation:

• Reason for Blackening: Silver reacts with sulfur compounds present in the air, such as hydrogen sulfide (H₂S), leading to the formation of silver sulfide (Ag₂S), a black-colored compound. This process is known as tarnishing or corrosion of silver.

• Chemical Reaction: The reaction can be represented as:

  2 Ag (silver) + H₂S (hydrogen sulfide) → Ag₂S (silver sulfide) + H₂ (hydrogen)

• Restoration of Shine: Rubbing the tarnished silver article with toothpaste removes the layer of silver sulfide, restoring the original luster of the silver. Toothpaste contains mild abrasives that effectively clean the tarnished surface.

The black substance formed on the silver article is silver sulfide, with the chemical formula Ag₂S. Regular cleaning can prevent tarnish buildup and maintain the shine of silver articles.