Chapter 1 · Question 11
What is corrosion? Explain with reference to the rusting of iron. Why are iron articles often painted, and how does it prevent corrosion?
Q11
What is corrosion? Explain with reference to the rusting of iron. Why are iron articles often painted, and how does it prevent corrosion?
Answer Revealed
Direct Answer:
Corrosion is the process in which a metal is attacked and damaged by substances in its environment such as moisture and acids. Rusting of iron is the most common example — when iron is exposed to moist air, it develops a reddish-brown powdery coating called rust. Iron articles are painted to create a protective barrier that prevents the metal surface from coming into direct contact with moisture and air, slowing or preventing corrosion.
Simple Explanation
Corrosion is nature's way of turning refined metals back to their natural ores. Rust is the reddish-brown, crumbly layer that forms on iron when it is left out in rain and humidity — it is basically hydrated iron oxide. Painting iron forms a shield — the paint blocks moisture and oxygen from reaching the metal surface, so the chemical reaction of rusting cannot even begin.
Exam-Ready Structure
Corrosion is the gradual damage of metals through reaction with substances around them, and rusting of iron is the most familiar example in this chapter: 1. Definition of corrosion: When a metal is attacked by substances around it such as moisture and acids, the metal is said to corrode, and this process is called corrosion. 2. Rusting of iron: (a) New iron articles are shiny, but when left exposed for some time they develop a reddish-brown powdery coating called rust. (b) Rusting is a corrosion process that damages objects made of iron. 3. Other examples of corrosion from the chapter: (a) Silver develops a black coating on exposure to air. (b) Copper develops a green coating on exposure to air. 4. Impact: Corrosion causes damage to car bodies, bridges, iron railings, ships, and many other objects made of metals, especially iron. 5. Prevention by painting: Painting coats the iron surface with a protective layer. This layer separates iron from the surrounding air and moisture, so the substances that cause corrosion cannot directly attack the iron surface.
Key Points
- Corrosion: slow deterioration of a metal by reaction with substances in its environment
- Rusting: iron articles develop a reddish-brown powdery coating when left exposed
- Corrosion damages car bodies, bridges, iron railings, ships, and other metal objects
- Silver develops a black coating and copper develops a green coating
- Painting prevents rusting by creating a barrier separating iron from moisture and oxygen
Related Questions
Q10
Define oxidation and reduction in terms of gain or loss of oxygen. Using the reaction of copper oxide with hydrogen, identify which substance is oxidised and which is reduced. Explain why this reaction is called a redox reaction.
Q12