Prevention of Corrosion - Class 10 Science

🛡️ Prevention of Corrosion

Class 10 Science | Metals and Non-metals | CBSE + Foundation + Competitive

🛡️ Prevention of Corrosion / संक्षारण की रोकथाम

1. What is Prevention of Corrosion? / संक्षारण की रोकथाम क्या है?

English:
Corrosion can damage metals and reduce their strength and useful life. Therefore, methods are used to prevent the contact of metal with oxygen, moisture and other corrosive substances. The main methods include:

• Painting
• Oiling and greasing
• Galvanisation
• Electroplating
• Alloying
• Cathodic protection

हिन्दी:
धातुओं को ऑक्सीजन, नमी तथा अन्य संक्षारक पदार्थों के संपर्क से बचाकर संक्षारण को रोका जा सकता है। इसके लिए पेंटिंग, तेल/ग्रीस लगाना, गैल्वनीकरण, विद्युत लेपन, मिश्रधातु निर्माण तथा कैथोडिक संरक्षण जैसी विधियों का उपयोग किया जाता है।

2. How Can Corrosion Be Prevented? / संक्षारण को कैसे रोका जा सकता है?

Method / विधि	How it prevents corrosion / कैसे रोकती है
Painting / पेंटिंग	Forms a protective barrier against air and moisture.
Oiling & Greasing / तेल एवं ग्रीस	Prevents contact with oxygen and moisture.
Galvanisation / गैल्वनीकरण	Coats iron with zinc.
Electroplating / विद्युत लेपन	Deposits a protective metal layer on another metal.
Alloying / मिश्रधातु निर्माण	Improves resistance to corrosion.

3. What is Galvanisation? / गैल्वनीकरण क्या है?

English:
Galvanisation is the process of coating iron or steel with a thin layer of zinc to protect it from corrosion. The zinc coating acts as a barrier between iron and the environment. Hindi:
लोहे या स्टील पर जिंक की पतली परत चढ़ाकर उसे संक्षारण से बचाने की प्रक्रिया को गैल्वनीकरण (Galvanisation) कहते हैं। इसमें जिंक की परत लोहे को वायु और नमी के सीधे संपर्क से बचाती है।

Iron/Steel + Zinc Coating → Protection from Corrosion

4. Why is Zinc Used in Galvanisation? / गैल्वनीकरण में जिंक का उपयोग क्यों?

Zinc is more reactive than iron. If the zinc coating is scratched, zinc can undergo oxidation preferentially and can provide sacrificial protection to the exposed iron under suitable conditions. Therefore, galvanisation can continue to protect iron even when a small area of coating is damaged.

⭐ Important CBSE Point:
Galvanisation is different from painting. Painting: Mainly provides a physical barrier. Galvanisation: Zinc provides a protective coating and can also offer sacrificial protection if the coating is damaged.

5. How Does Painting Prevent Rusting? / पेंटिंग जंग लगने से कैसे रोकती है?

English:
Paint forms a continuous protective layer over the iron surface. This layer prevents oxygen and moisture from directly reaching the iron surface. Since oxygen and moisture are required for ordinary rusting, the paint reduces the possibility of rust formation.

हिन्दी:
पेंट लोहे की सतह पर एक सुरक्षात्मक परत बना देता है। यह परत ऑक्सीजन और नमी को लोहे की सतह तक पहुँचने से रोकती है। चूँकि सामान्य रूप से जंग लगने के लिए ऑक्सीजन और नमी दोनों आवश्यक हैं, इसलिए पेंटिंग जंग लगने को रोकती है।

Iron Surface + Paint Layer → No Direct Contact with Air & Moisture

6. Important Methods of Corrosion Prevention / संक्षारण रोकने की प्रमुख विधियाँ

1. Painting: Used for gates, bridges, railings and metal structures.

2. Oiling and Greasing: Used for machine parts, tools and moving components.

3. Galvanisation: Used for iron sheets, pipes, wires and many steel products.

4. Electroplating: A protective metal coating is deposited using electrolysis.

5. Alloying: Certain alloy compositions improve corrosion resistance.

6. Cathodic Protection: The metal to be protected is made the cathode of an electrochemical system.

7. Why Should Paint Be Reapplied? / पेंट को दोबारा क्यों लगाया जाता है?

If the paint layer gets scratched, cracked or peeled off, the exposed iron can come into contact with oxygen and moisture. Therefore, damaged paint should be repaired or reapplied.

Damaged Paint → Exposed Iron → Oxygen + Moisture → Rusting

8. Galvanisation vs Painting / गैल्वनीकरण एवं पेंटिंग में अंतर

Painting	Galvanisation
Paint is applied on the surface.	Zinc coating is applied to iron/steel.
Mainly acts as a barrier.	Acts as barrier and can provide sacrificial protection.
Damaged paint exposes iron.	Zinc can protect exposed iron under suitable conditions.
Requires periodic maintenance.	Zinc coating can provide relatively durable protection.

9. 30 MCQs / बहुविकल्पीय प्रश्न

Q1. Which of the following is a method of preventing corrosion?
संक्षारण रोकने की विधि कौन-सी है?

A. Painting

B. Scratching

C. Heating iron in air

D. Keeping iron wet

Answer: A

Q2. Galvanisation involves coating iron with:

A. Copper

B. Zinc

C. Silver

D. Aluminium oxide

Answer: B

Q3. The main purpose of painting iron is to:

A. Increase its melting point

B. Prevent contact with air and moisture

C. Make it magnetic

D. Increase its density

Answer: B

Q4. Which metal is used for galvanising iron?

A. Zinc

B. Gold

C. Silver

D. Mercury

Answer: A

Q5. Galvanisation protects iron mainly by:

A. Coating it with zinc

B. Melting the iron

C. Removing all oxygen from air

D. Converting iron into copper

Answer: A

Q6. Which substance is commonly used to protect machine parts from corrosion?

A. Water

B. Oil or grease

C. Salt

D. Acid

Answer: B

Q7. Painting prevents rusting by preventing contact between iron and:

A. Oxygen and moisture

B. Nitrogen only

C. Hydrogen only

D. Carbon only

Answer: A

Q8. Zinc is used for galvanisation because it:

A. Is less reactive than gold

B. Provides a protective coating and can offer sacrificial protection

C. Always dissolves immediately

D. Is a non-metal

Answer: B

Q9. Which method is especially suitable for protecting iron sheets?

A. Galvanisation

B. Soaking in water

C. Heating in oxygen

D. Adding salt

Answer: A

Q10. Which of the following does NOT prevent corrosion?

A. Oiling

B. Painting

C. Galvanisation

D. Keeping iron continuously wet

Answer: D

Q11. The protective layer in galvanisation is made of:

A. Zinc

B. Iron

C. Carbon

D. Sulphur

Answer: A

Q12. If paint on an iron gate is scratched deeply:

A. Iron becomes completely immune to corrosion

B. Exposed iron can start corroding

C. Iron becomes gold

D. Rusting becomes impossible

Answer: B

Q13. Which method uses a protective metal coating?

A. Galvanisation

B. Drying

C. Cutting

D. Heating

Answer: A

Q14. Which method can provide sacrificial protection to iron?

A. Galvanisation with zinc

B. Painting with water

C. Washing with acid

D. Heating with oxygen

Answer: A

Q15. Corrosion can be prevented by:

A. Isolating the metal from corrosive agents

B. Increasing moisture

C. Adding salt water

D. Exposing metal to humid air

Answer: A

Q16. Oiling and greasing prevent corrosion by:

A. Creating a protective barrier

B. Producing oxygen

C. Producing rust

D. Increasing humidity

Answer: A

Q17. Which process deposits a metal coating using electricity?

A. Electroplating

B. Filtration

C. Distillation

D. Sedimentation

Answer: A

Q18. Painting is effective against rusting as long as:

A. The coating remains intact

B. The iron is kept wet

C. Salt is added

D. The paint is removed

Answer: A

Q19. Which is an example of corrosion prevention?

A. Galvanising an iron sheet

B. Leaving iron in rain

C. Adding salt to iron

D. Scratching an iron surface

Answer: A

Q20. Zinc protects iron partly because zinc is:

A. More reactive than iron

B. Less reactive than gold

C. A noble gas

D. A non-metal

Answer: A

Q21. Which method is commonly used for protecting iron gates?

A. Painting

B. Adding water

C. Adding salt

D. Removing all coating

Answer: A

Q22. Which method is commonly used to protect underground or moving machine components?

A. Oiling/greasing

B. Washing with salt

C. Exposing to moisture

D. Scratching

Answer: A

Q23. What happens if the zinc coating is damaged?

A. Zinc may still provide sacrificial protection to exposed iron under suitable conditions

B. Iron becomes a non-metal

C. Iron immediately melts

D. Oxygen disappears

Answer: A

Q24. Which method changes the composition of a metal to improve corrosion resistance?

A. Alloying

B. Painting

C. Oiling

D. Washing

Answer: A

Q25. Which of the following is a barrier method?

A. Painting

B. Scratching

C. Heating

D. Rusting

Answer: A

Q26. The main corrosive agents responsible for ordinary rusting are:

A. Oxygen and moisture

B. Nitrogen and helium

C. Hydrogen and nitrogen

D. Carbon and hydrogen

Answer: A

Q27. Why should damaged paint be repaired?

A. To prevent exposed metal from contacting air and moisture

B. To increase rusting

C. To increase salt content

D. To dissolve the metal

Answer: A

Q28. Which one is NOT a corrosion prevention technique?

A. Galvanisation

B. Painting

C. Oiling

D. Keeping iron in moist air

Answer: D

Q29. In galvanisation, the iron is coated with:

A. Zinc

B. Copper sulphate solution only

C. Sodium chloride

D. Water

Answer: A

Q30. The fundamental idea behind painting, oiling and galvanisation is to:

A. Reduce the contact of iron with corrosive surroundings

B. Increase moisture

C. Increase oxygen supply

D. Produce rust faster

Answer: A

10. 30 Subjective Questions with Answers / व्यक्तिपरक प्रश्न

1 Mark
Q1. How can corrosion be prevented?

Answer: Corrosion can be prevented by painting, oiling, greasing, galvanisation, electroplating and alloying.

1 Mark
Q2. What is galvanisation?

Answer: Galvanisation is the process of coating iron or steel with zinc to prevent corrosion.

1 Mark
Q3. Which metal is used for galvanising iron?

Answer: Zinc.

1 Mark
Q4. How does painting prevent rusting?

Answer: Paint forms a protective layer that prevents oxygen and moisture from reaching the iron surface.

1 Mark
Q5. Name one method other than painting used to prevent corrosion.

Answer: Galvanisation.

2 Marks
Q6. Why is iron painted?

Answer: Painting prevents direct contact of iron with oxygen and moisture, thereby reducing rusting.

2 Marks
Q7. What is the role of zinc in galvanisation?

Answer: Zinc forms a protective coating over iron and can provide sacrificial protection if the coating is damaged under suitable conditions.

2 Marks
Q8. Why does painting stop rusting?

Answer: Paint acts as a barrier and prevents oxygen and water from reaching the iron surface.

2 Marks
Q9. Name two methods of preventing corrosion.

Answer: Painting and galvanisation.

2 Marks
Q10. What happens when paint on an iron object gets scratched?

Answer: The exposed iron can come into contact with oxygen and moisture and may start rusting.

3 Marks
Q11. Explain galvanisation.

Answer:
Galvanisation is the process of coating iron or steel with a thin layer of zinc. The zinc coating prevents direct contact between iron and the environment and can also provide sacrificial protection when suitably exposed.

3 Marks
Q12. Explain how painting prevents rusting.

Answer:
1. Paint forms a protective coating.
2. It prevents oxygen from reaching iron.
3. It also prevents moisture from reaching iron.
4. Therefore, the conditions required for ordinary rusting are reduced.

3 Marks
Q13. Why is galvanisation more than just a barrier coating?

Answer: Zinc provides a physical barrier to the environment. Since zinc is more reactive than iron, it can also oxidise preferentially and provide sacrificial protection to exposed iron under suitable conditions.

3 Marks
Q14. Give three methods of preventing corrosion.

Answer:
1. Painting
2. Galvanisation
3. Oiling and greasing

3 Marks
Q15. Why should paint be reapplied on iron objects?

Answer: Paint may crack, peel or get scratched with time. Repainting restores the protective barrier and prevents oxygen and moisture from reaching the exposed iron.

4 Marks
Q16. Explain four methods of preventing corrosion.

Answer:
1. Painting: Provides a barrier against oxygen and moisture.
2. Oiling: Forms a protective film over the metal.
3. Galvanisation: Coats iron with zinc.
4. Electroplating: Deposits a protective metal coating using electricity.

4 Marks
Q17. Differentiate between painting and galvanisation.

Painting	Galvanisation
Paint is applied to the surface.	Zinc is coated on iron/steel.
Mainly acts as a barrier.	Acts as barrier and may provide sacrificial protection.
Scratches can expose iron.	Zinc can protect exposed iron under suitable conditions.

4 Marks
Q18. Why is zinc suitable for protecting iron?

Answer:
1. Zinc can form a protective coating over iron.
2. It prevents direct contact with air and moisture.
3. Zinc is more reactive than iron.
4. It can therefore provide sacrificial protection to exposed iron under suitable conditions.

4 Marks
Q19. Why does oiling prevent corrosion of machine parts?

Answer: Oil forms a continuous protective film on the metal surface. This reduces contact between the metal, oxygen and moisture, thereby reducing corrosion.

4 Marks
Q20. Why does a scratched painted iron surface rust?

Answer: Scratching removes the protective paint layer and exposes the iron. The exposed iron can then contact oxygen and moisture, allowing rusting to occur.

5 Marks
Q21. Explain the importance of galvanisation in preventing corrosion.

Answer:
Galvanisation protects iron by coating it with zinc. The zinc layer separates iron from air and moisture. Zinc is more reactive than iron and can undergo oxidation preferentially when exposed. Thus galvanisation provides both barrier protection and, under suitable conditions, sacrificial protection.

5 Marks
Q22. Explain why painting is an effective method for preventing rusting.

Answer:
Painting forms a protective layer over iron. This layer prevents oxygen and moisture from directly contacting the iron surface. Since both oxygen and moisture are required for ordinary rusting, painting greatly reduces rust formation. However, damaged paint must be repaired.

5 Marks
Q23. Explain the difference between barrier protection and sacrificial protection.

Answer:
Barrier protection: A coating prevents the metal from coming into contact with corrosive substances. Painting and oiling are examples. Sacrificial protection: A more reactive metal is used to protect the metal that needs protection. Zinc on iron in galvanisation can provide sacrificial protection under suitable conditions.

5 Marks
Q24. Why is corrosion prevention important?

Answer: Corrosion weakens metals, reduces their useful life and causes economic losses. Preventing corrosion improves safety, durability and reduces repair and replacement costs.

5 Marks
Q25. Explain five methods used to prevent corrosion.

Answer:
1. Painting
2. Oiling and greasing
3. Galvanisation
4. Electroplating
5. Alloying

These methods either isolate the metal from corrosive substances or improve its corrosion resistance.

6 Marks
Q26. Explain galvanisation of iron in detail.

Answer:
Galvanisation is the process of coating iron or steel with zinc. The zinc layer acts as a barrier between iron and oxygen/moisture. Zinc is also more reactive than iron, so if the coating is damaged, zinc can oxidise preferentially and provide sacrificial protection under suitable conditions. Therefore galvanisation provides effective protection against corrosion.

6 Marks
Q27. Explain how painting, oiling and galvanisation prevent corrosion.

Answer:
Painting: Forms a protective barrier between iron and air/moisture.

Oiling: Forms a water-repellent protective film over the metal.

Galvanisation: Covers iron with zinc. Zinc provides barrier protection and may also provide sacrificial protection when the coating is damaged.

6 Marks
Q28. A painted iron gate develops rust after the paint is damaged. Explain why.

Answer:
The paint normally prevents oxygen and moisture from reaching iron. When the paint is damaged, the underlying iron becomes exposed to air and moisture. The exposed iron undergoes electrochemical corrosion and forms rust. Therefore damaged paint should be repaired quickly to restore the protective barrier.

6 Marks
Q29. Compare different methods of corrosion prevention.

Method	Protection Mechanism
Painting	Barrier against air and moisture
Oiling/Greasing	Protective film
Galvanisation	Zinc coating + possible sacrificial protection
Electroplating	Protective metal coating
Alloying	Improves corrosion resistance through composition

6 Marks
Q30. "Galvanisation is better than painting for certain applications." Explain.

Answer:
Painting mainly provides barrier protection and depends on the paint layer remaining intact. Galvanisation coats iron with zinc. Zinc not only separates iron from the environment but can also provide sacrificial protection if the coating is damaged under suitable conditions. Therefore galvanisation can provide more durable protection in many applications such as iron sheets, pipes and steel products.

11. Quick Revision / त्वरित पुनरावृत्ति

Corrosion Prevention → Block Contact with Oxygen + Moisture

Painting → Protective Barrier

Oiling/Greasing → Protective Film

Galvanisation → Zinc Coating on Iron/Steel

Zinc → Barrier + Sacrificial Protection under suitable conditions

Damaged Paint → Exposed Iron → Rusting

⭐ CBSE Exam Booster:

Q. What is galvanisation?
Coating iron/steel with zinc to prevent corrosion.

Q. How does painting prevent rusting?
It prevents oxygen and moisture from reaching iron.

Q. Which metal is used in galvanisation?
Zinc.

Q. Why is zinc useful?
It provides a protective coating and can offer sacrificial protection to exposed iron under suitable conditions.