Question

(a) Explain the term "corrosion" with an example. Write a chemical equation to show the process of corrosion of iron.
(b) What special name is given to the corrosion of iron?
(c) What type of chemical reaction is involved in the corrosion of iron?
(d) Name any three objects (or structures) which are gradually damaged by the corrosion of iron and steel.

Answer 1

(a) Corrosion is the process by which a metal corrodes when it comes in contact with its surroundings such as moisture, air and acids, for example, powdered (brown) coating on iron objects such as iron railings.
In corrosion, oxidation of iron takes place.
Fe (s) → Fe²⁺ (aq) + 2e⁻​

Iron supplies electrons at the edge of the droplet to reduce oxygen from the air.
O₂ (g) + 2H₂O (l) + 4e⁻ → 4OH⁻ (aq)

Within the droplet, the hydroxide ions react with the iron(II) ions and iron(II) hydroxide is precipitated.

Fe²⁺ (aq) + 2OH⁻ (aq) → Fe(OH)₂ (s)

Rust is then quickly produced by the oxidation of the precipitate.

4Fe(OH)₂ (s) + O₂ (g) → 2Fe₂O₃ • H₂O (s) + 2H₂O (l)

(b) Corrosion of iron is called rust.

(c) Redox reaction is involved in the corrosion of iron.

(d) Following are the three objects that are damaged by corrosion:
(i) Iron railings
(ii) Ships
(iii) Bridges