Copper exposed to air and water may be oxidized. The green oxidized product is referred to as "patina". (a) Write a balanced chemical equation to show the reaction of copper to copper (II) ions with oxygen and protons from acid rain. (b) Would you expect some kind of "patina" on a silver surface? Explain.

To write a balanced chemical equation for the reaction of copper (Cu) to form copper (II) ions (Cu²⁺), we need to consider the involvement of oxygen (O₂) and protons (H⁺) from acid rain. The reaction can be divided into two half-reactions: oxidation of copper and reduction of oxygen. For oxidation of copper: Cu → Cu²⁺ + 2e⁻ For the reduction of oxygen, considering the protons (H⁺) from acid rain: O₂ + 4e⁻ + 4H⁺ → 2H₂O Now, we will balance the electrons by multiplying the first half-reaction by 2: 2Cu → 2Cu²⁺ + 4e⁻ O₂ + 4e⁻ + 4H⁺ → 2H₂O Next, we will add these half-reactions together to create the overall balanced equation: 2Cu + O₂ + 4H⁺ → 2Cu²⁺ + 2H₂O So the balanced chemical equation is: 2Cu + O₂ + 4H⁺ → 2Cu²⁺ + 2H₂O

The greenish "patina" that forms on copper surfaces is primarily due to the formation of copper(II) carbonate (CuCO₃) and copper(II) hydroxide (Cu(OH)₂). Silver undergoes a different oxidation process in which it reacts with sulfur compounds, such as hydrogen sulfide (H₂S) that might be present in the atmosphere. This results in a blackish tarnish, silver sulfide (Ag₂S), on the surface rather than a green patina like copper. Therefore, we can expect a tarnished, black surface on silver, but not a green "patina" similar to that on copper surfaces.