the formation of a layer of cupric oxide on the surface of copper.
the formation of a layer of basic carbonate of copper on the surface of copper.
the formation of a layer of cupric hydroxide on the surface of copper.
the formation of basic copper sulphate layer on the surface of the metal.
Show Solution
The Correct Option isB
Solution and Explanation
The question addresses why copper turns green when exposed to moist air over time. Let's analyze the options and find out the correct reasoning.
Formation of a layer of cupric oxide on the surface of copper: Cupric oxide is black in color. When copper reacts with oxygen, it initially forms a layer of copper oxide which is black. Thus, this does not explain the green coloration.
Formation of a layer of basic carbonate of copper on the surface of copper: This is the correct answer. In the presence of carbon dioxide and water in the air, copper reacts over time to form a green patina known as copper carbonate, specifically basic copper carbonate (\text{Cu}_2(\text{OH})_2\text{CO}_3), which gives copper its characteristic green color. This process is known as patination.
Formation of a layer of cupric hydroxide on the surface of copper: Cupric hydroxide is blue, not green. While it may initially form as an intermediate stage, it does not explain the long-term green color.
Formation of basic copper sulphate layer on the surface of the metal: Copper sulphate compounds are not the typical result of copper exposure to moist air. Sulphates primarily form in the presence of sulfur compounds, not just moisture and carbon dioxide.
To summarize, when copper is exposed to moist air, it forms a green layer due to the formation of basic copper carbonate. This process of patination is what leads to the characteristic green color observed on copper surfaces exposed to weather over long periods.
