Corrosion is the natural process of deterioration of a metal due to chemical or electrochemical reactions with its environment. This process leads to the oxidation of the metal, causing structural damage to items like bridges and iron infrastructure.
2572
Which metal develops a green-colored coating of basic carbonate when exposed to moist air over time?
When copper is exposed to moist air containing carbon dioxide and oxygen, it undergoes a slow corrosion process. This results in the formation of a green patina, which is a mixture of copper(II) carbonate and copper(II) hydroxide, chemically represented as CuCO3·Cu(OH)2. This layer protects the underlying metal from further corrosion.
2573
When copper is exposed to moist air, it develops a green coating. What is the chemical composition of this substance?
The green coating on copper, often called patina, is primarily composed of basic copper carbonate, CuCO3·Cu(OH)2. This forms when copper reacts with atmospheric oxygen, carbon dioxide, and moisture over time. This protective layer prevents further corrosion of the underlying metal.
2574
When an iron sheet is exposed to moist air, it develops rust. How is rust classified?
Rust is chemically defined as hydrated iron(III) oxide (Fe2O3·nH2O). Because it has a fixed chemical composition formed by the reaction of iron with oxygen and water, it is classified as a chemical compound rather than a simple mixture or an element.
2575
Why is zinc used in the galvanization process to protect iron from corrosion?
Zinc is more electropositive (more reactive) than iron. In galvanization, zinc acts as a sacrificial anode. Even if the coating is scratched, the zinc will oxidize preferentially to the iron, thereby preventing the iron from rusting.
2576
What is the chemical term for the reddish-brown substance that forms on the surface of iron when exposed to moist air?
When iron is exposed to oxygen and moisture, it undergoes an electrochemical oxidation process known as corrosion. The resulting hydrated iron(III) oxide, Fe2O3·nH2O, is commonly referred to as rust. This process weakens the structural integrity of the metal over time.
2577
How is galvanized iron defined in the context of material science?
Galvanized iron refers to iron or steel sheets that have been coated with a layer of zinc. This coating is applied through hot-dipping or electroplating to protect the base metal from oxidation and environmental degradation, significantly extending the lifespan of the material.
2578
Why are food cans typically coated with tin rather than zinc?
Zinc is more chemically reactive than tin. If zinc were used to coat food cans, it would react more readily with acidic food components, potentially leaching into the food and causing toxicity. Tin is less reactive and provides a safer, more stable protective barrier.
2579
Which metal is commonly used for plating to protect iron from corrosion through sacrificial protection?
Zinc plating, also known as galvanization, protects iron from corrosion because zinc is more reactive than iron. In the presence of moisture and oxygen, the zinc acts as a sacrificial anode, oxidizing in preference to the iron. Even if the coating is scratched, the zinc continues to protect the underlying iron through electrochemical action, whereas metals like tin would accelerate iron corrosion if the coating were breached.
2580
What substance in the atmosphere is primarily responsible for the tarnishing or corrosion of silver?
Silver tarnishes when it reacts with hydrogen sulfide (H2S) present in the air, forming a layer of black silver sulfide (Ag2S). This is a chemical corrosion process. While silver can react with oxygen at high temperatures, the common tarnish observed on silver jewelry and utensils at room temperature is predominantly due to the reaction with sulfur-containing compounds in the environment.
