The correct sequence of steps during the corrosion of iron is
(A) Ferrous ions are oxidized by atmospheric oxygen
(B) Hydrated ferric oxide $(FeO_3.xH_2O)$ formed with production of $H^+$ ions
(C) At a particular spot of iron object, oxidation takes place and that spot behaves as anode
(D) Electron released at anode moves through metal and reduces oxygen in the presence of $H^+$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (C), (D), (A), (B)
Corrosion of iron (rusting) is an electrochemical process that occurs in the presence of moisture and oxygen. The process involves oxidation at the anode and reduction at the cathode.
Step 1: Formation of anodic region
At certain spots on the iron surface, oxidation occurs. Fe → Fe²⁺ + 2e⁻
These regions behave as anodes. Thus, (C) occurs first.
STep 2: Reduction of oxygen
The electrons released at the anode move through the metal to another region where oxygen is reduced.
O₂ + 4H⁺ + 4e⁻ → 2H₂O Thus, (D) occurs next.
Step 3: Oxidation of ferrous ions
The ferrous ions formed are further oxidized by atmospheric oxygen to ferric ions. Thus, (A) occurs next.
Step 4: Formation of rust
Ferric ions combine with water to form hydrated ferric oxide, commonly called rust. Fe₂O₃ · xH₂O
Thus, (B) occurs last.