In Chemistry, Corrosion & its Prevention is an important Industrial Chemistry topic. ECET exams often include direct and conceptual questions from this area.
📘 Concept Notes
🌍 What is Corrosion?
- Corrosion is the gradual deterioration of metals due to chemical or electrochemical reaction with the environment.
- Common example: Rusting of iron when exposed to air and moisture.
General Reaction of Iron Rusting:
On drying, it forms:
⚙️ Types of Corrosion
- Dry Corrosion (Chemical):
- Direct reaction with gases (O₂, SO₂, Cl₂).
- Example: Tarnishing of silver.
- Wet Corrosion (Electrochemical):
- In presence of moisture/electrolytes.
- Involves formation of anodic & cathodic areas.
- Example: Rusting of iron.
🔋 Electrochemical Mechanism of Rusting
Anodic reaction:
Cathodic reaction:
Overall:
Fe²⁺ combines with OH⁻ → Fe(OH)₂ → oxidizes to Fe(OH)₃ → rust.
🛡️ Prevention of Corrosion
- Barrier Protection – Applying oil, grease, paint, plastic coating.
- Galvanization – Coating iron with zinc.
- Electroplating – Depositing a thin layer of another metal (e.g., nickel, chromium).
- Cathodic Protection – Connecting iron to more active metal (Zn/Mg acts as sacrificial anode).
- Alloying – Stainless steel resists corrosion better than pure iron.
🔟 10 Expected MCQs – ECET 2026
Q1. Corrosion of iron is commonly known as:
A) Tarnishing
B) Rusting
C) Scaling
D) Patina
Q2. The chemical formula of rust is:
A) FeO
B) Fe₂O₃·xH₂O
C) Fe₃O₄
D) Fe(OH)₂
Q3. Wet corrosion is also called:
A) Electrochemical corrosion
B) Dry corrosion
C) High temperature oxidation
D) None
Q4. The anodic reaction in rusting of iron is:
A) Fe → Fe²⁺ + 2e⁻
B) O₂ + 4H⁺ + 4e⁻ → 2H₂O
C) Fe²⁺ → Fe³⁺
D) Fe³⁺ + e⁻ → Fe²⁺
Q5. Which method uses Zn coating to protect iron?
A) Electroplating
B) Galvanization
C) Cathodic protection
D) Alloying
Q6. Stainless steel resists corrosion mainly because:
A) It contains chromium
B) It contains copper
C) It contains aluminium
D) It contains zinc
Q7. Which of the following is NOT a prevention method?
A) Painting
B) Oiling
C) Galvanization
D) Heating
Q8. In cathodic protection, the metal connected to iron acts as:
A) Cathode
B) Anode
C) Neutral
D) Alloy
Q9. Dry corrosion occurs due to:
A) Moisture
B) Electrolyte
C) Direct chemical reaction with gases
D) Salt solution
Q10. Which gas accelerates rusting in presence of water?
A) Oxygen
B) Hydrogen
C) Carbon dioxide
D) Nitrogen
✅ Answer Key
| Q.No | Answer |
|---|---|
| Q1 | B |
| Q2 | B |
| Q3 | A |
| Q4 | A |
| Q5 | B |
| Q6 | A |
| Q7 | D |
| Q8 | B |
| Q9 | C |
| Q10 | A |
🧠 Explanations
- Q1 → B: Corrosion of iron = Rusting.
- Q2 → B: Rust = Fe₂O₃·xH₂O.
- Q3 → A: Wet corrosion involves electrochemical reactions.
- Q4 → A: At anode, Fe oxidizes to Fe²⁺.
- Q5 → B: Galvanization = Zn coating.
- Q6 → A: Chromium forms passive oxide film.
- Q7 → D: Heating does not prevent corrosion.
- Q8 → B: Sacrificial metal acts as anode.
- Q9 → C: Dry corrosion = chemical attack by gases.
- Q10 → A: O₂ is essential for rusting.
🎯 Why Practice Matters
Corrosion is industrially important because it causes huge economic losses. In ECET, questions are asked on mechanism, prevention methods, and formulas. Practicing MCQs ensures accuracy in exam.
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