Lemon and tamarind juice effectively clean tarnished copper vessels because they contain acids that react with and dissolve the layer of copper carbonate or copper oxide that causes the tarnish. Specifically, the citric acid in lemon and tartaric acid in tamarind neutralize the basic copper carbonate and form soluble salts, which can then be washed away, revealing the shiny copper surface.
Here’s a more detailed explanation:
Tarnish Formation:
Copper reacts with moist air, particularly carbon dioxide, forming a layer of copper carbonate (Cu2(OH)2CO3) on its surface, which is responsible for the green or brown tarnish.
Acidic Reaction:
The citric acid in lemon and the tartaric acid in tamarind are acidic and react with the basic copper carbonate.
Neutralization and Dissolution:
The acid neutralizes the base (copper carbonate) and dissolves the layer, forming soluble salts like copper acetate (with citric acid) or copper tartarate (with tartaric acid).
Removal of Salts:
These soluble salts are easily washed away with water, leaving the copper surface clean and shiny.