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On oxidation, silver changes its colour to _______ and copper changes its colour to _______.
grey; green
black; green
black; blue
grey; blue
black; green
On exposure to air and moisture, silver undergoes oxidation/tarnishing to form a black coating of silver sulfide (Ag2тАЛS), while copper undergoes corrosion/oxidation forming a green layer of basic copper carbonate (CuCO3тАЛтЛЕCu(OH)2тАЛ). Therefore, silver turns black and copper turns green upon oxidation.
On exposure to air and moisture, silver undergoes oxidation/tarnishing to form a black coating of silver sulfide (Ag2тАЛS), while copper undergoes corrosion/oxidation forming a green layer of basic copper carbonate (CuCO3тАЛтЛЕCu(OH)2тАЛ). Therefore, silver turns black and copper turns green upon oxidation.
Think of old silver jewelry or silverware getting a dull black tarnish over time, while historical copper statues (like the Statue of Liberty) or old copper coins turn greenish when exposed to outdoor weather for years.
Remember 'S-B-C-G': Silver turns Black, Copper turns Green.
4Ag+2H2тАЛS+O2тАЛтЖТ2Ag2тАЛS+2H2тАЛO тАФ Oxidation of Silver forming Black Silver Sulfide
2Cu+H2тАЛO+CO2тАЛ+O2тАЛтЖТCuCO3тАЛтЛЕCu(OH)2тАЛ тАФ Atmospheric Corrosion of Copper forming Green Basic Copper Carbonate
Silver reacts with atmospheric hydrogen sulfide (H2тАЛS) in the presence of oxygen to form black silver sulfide: 4Ag+2H2тАЛS+O2тАЛтЖТ2Ag2тАЛS+2H2тАЛO. Copper reacts slowly with atmospheric carbon dioxide, water vapour, and oxygen to form a green coating of basic copper carbonate: 2Cu+H2тАЛO+CO2тАЛ+O2тАЛтЖТCuCO3тАЛтЛЕCu(OH)2тАЛ.
Silver tarnishing is caused specifically by traces of hydrogen sulfide (H2тАЛS) gas present in the air.
Copper corrosion yields a green mixture containing copper carbonate and copper hydroxide, often called 'patina'.
Iron corrosion (rusting) produces reddish-brown hydrated ferric oxide (Fe2тАЛO3тАЛтЛЕxH2тАЛO).
Understanding atmospheric corrosion prevention and electroplating.
Preservation of metallic heritage artifacts and monuments like copper domes and statues.
Option A (grey; green) is incorrect because pure silver turns black, not grey, when tarnished.
Option C (black; blue) is incorrect because hydrated copper sulfate is blue, but atmospheric copper corrosion forms a green compound.
Option D (grey; blue) is incorrect on both counts.
B is correct тАФ Silver turns black due to the formation of silver sulfide (Ag2тАЛS), while copper turns green due to basic copper carbonate (CuCO3тАЛтЛЕCu(OH)2тАЛ).
Questions on metal corrosion frequently compare iron (reddish-brown rust), silver (black tarnish), and copper (green patina). Memorize the chemical formula for green copper layer (CuCO3тАЛтЛЕCu(OH)2тАЛ) as it is a favorite in exams.
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