NCERT Line-by-Line
1. TITLE
"NCERT says 'The ferrous ions are further oxidised by atmospheric oxygen to ferric ions' — Here's how NEET tests it"
2. THE NCERT STATEMENT
NCERT EXACT LINE:
"At a particular spot of an object made of iron, oxidation takes place and that spot behaves as anode and we can write the reaction Oxidation: $Fe(s) \rightarrow Fe^{2+}(aq) + 2e^{-}$... The ferrous ions are further oxidised by atmospheric oxygen to ferric ions which come out as rust in the form of hydrated ferric oxide ($Fe_{2}O_{3} \cdot xH_{2}O$) and with further production of hydrogen ions."
— NCERT Class 12, Chapter 2 (Electrochemistry), Pages 56-57
3. WHY THIS LINE MATTERS
- How many times has NEET tested this? It is a highly tested concept because corrosion is a classic, real-world electrochemical phenomenon. Questions frequently appear directly asking for the formula of rust or the specific half-cell reactions.
- What makes this statement tricky? It outlines a two-step oxidation process. Students often assume rust is formed immediately at the anode, missing the fact that the initial anodic product is ferrous ($Fe^{2+}$), not ferric ($Fe^{3+}$).
- What do students typically misremember? They frequently mix up the oxidation states of iron, forgetting whether rust is a ferrous oxide or a ferric oxide.
4. MCQ (Directly from this NCERT line)
According to NCERT, which of the following correctly describes the chemical process involved in the formation of rust?
A) Ferrous ions are further oxidised by atmospheric oxygen to ferric ions, forming hydrated ferric oxide.
B) Ferrous ions are further reduced by atmospheric oxygen to ferric ions, forming hydrated ferric oxide.
C) Iron (Fe) is directly oxidised by atmospheric oxygen to ferric oxide at the anodic spot.
D) Ferric ions are reduced by atmospheric oxygen to ferrous ions, forming hydrated ferric oxide.
5. ANSWER + LINE BREAKDOWN
Correct Answer: A
Break down the NCERT line:
- "At a particular spot... that spot behaves as anode" means that pure metallic iron ($Fe$) is initially oxidized to ferrous ions ($Fe^{2+}$) at a specific localized region.
- "The ferrous ions are further oxidised... to ferric ions" means the $Fe^{2+}$ ions undergo a secondary oxidation step to $Fe^{3+}$.
- "by atmospheric oxygen" means that the $O_2$ in the air acts as the final oxidizing agent in this secondary step.
- The key word is "further" because it clarifies that rusting isn't a single reaction; iron must first become ferrous ($Fe^{2+}$) electrochemically before it can become the ferric ($Fe^{3+}$) compound known as rust.
6. HOW NEET TWISTS THIS
Show 3 ways NEET can ask the same fact:
- As direct question: "What is the chemical composition of rust formed during the corrosion of iron?" (Answer: Hydrated ferric oxide / $Fe_{2}O_{3} \cdot xH_{2}O$).
- As assertion-reason: Assertion: Rusting of iron involves oxidation occurring at the anodic spot. Reason: Iron is directly converted to $Fe_{2}O_{3} \cdot xH_{2}O$ at the anode. (Answer: Assertion is true, but Reason is false—it forms $Fe^{2+}$ first).
- As match the following: Matching "Anodic Reaction" with "$Fe \rightarrow Fe^{2+} + 2e^{-}$" and matching "Rust" with "Hydrated ferric oxide".
7. MEMORY LOCK
MEMORIZE:
Iron starts at 0, goes to +2 at the Anode, then +3 in the Rust.
Mnemonic: Anode is Always Ferrous (+2), Rust is Really Ferric (+3).
8. RELATED NCERT LINES
Also remember these from the same page:
- "Electrons released at anodic spot move through the metal and go to another spot on the metal and reduce oxygen in the presence of $H^{+}$..."
- "This spot behaves as cathode with the reaction: $O_{2}(g) + 4H^{+}(aq) + 4e^{-} \rightarrow 2H_{2}O(l)$"
9. NCERT REFERENCE
NCERT Class 12, Chapter 2 (Electrochemistry), Pages 56-57, Paragraph under "2.8 Corrosion".
10. CTA
All important NCERT lines from this chapter → Redox Reactions & Electrochemistry Guide