Case Study:

In a coastal town in Kerala, iron grills and gates installed in houses start developing a reddish-brown layer within a few months. Residents notice that homes closer to the sea experience faster rusting compared to those located farther inland. Similarly, an old iron bridge in a village near the Ganga river shows signs of weakening due to corrosion.

Rusting is a slow chemical change that occurs when iron reacts with oxygen in the presence of moisture. The reddish-brown substance formed is called rust. High humidity in coastal regions increases the amount of water vapour in the air, accelerating the process. Salt present in sea air further increases the rate of rusting by making water more conductive.

In an experiment conducted in a Class 9 lab, three iron nails were placed in:

1. Dry air (with calcium chloride to absorb moisture)
2. Boiled water covered with oil (to prevent contact with air)
3. Normal tap water exposed to air

After three days, only the nail in tap water exposed to air showed rusting. This proves that both oxygen and water are necessary conditions for rusting.

To prevent rusting, methods such as painting, galvanization (coating with zinc), and oiling are commonly used. Indian Railways regularly paints iron tracks and bridges to protect them from corrosion and ensure safety.

Questions:

Section A - MCQs

1. Iron grills near the sea rust faster mainly because:
A. Temperature is higher near the sea
B. Salt in air increases moisture’s effect
C. Iron quality is poor
D. Sunlight causes rusting

2. In the laboratory experiment, the nail in boiled water covered with oil did not rust because:
A. Water prevents rusting
B. Oil reacts with iron
C. Oxygen was not available
D. Temperature was low

3. Which condition is essential for rusting?
A. Oxygen only
B. Water only
C. Both oxygen and water
D. Carbon dioxide only

4. Galvanization protects iron from rusting by:
A. Cooling the iron surface
B. Increasing hardness
C. Coating iron with zinc
D. Removing moisture permanently

Section B - Short Answer Questions

1. Why do iron objects rust faster during the monsoon season in India? Explain scientifically.
2. In the experiment, why was boiled water used instead of normal water for the second nail?
3. Suggest two practical methods to prevent rusting of an iron water tank installed on a rooftop and justify your answer.

Section C - Long Answer Question

1. An iron pipeline supplying water in a village develops rust after 5 years. The panchayat plans to either paint the pipe every year or replace it with galvanized iron pipes.
(a) Compare both methods scientifically.
(b) Which option would be more durable and why?
(c) What could happen if rusting is ignored for a long period?

Answer Key:

Section A - MCQs

1. B
2. C
3. C
4. C

Section B - Short Answers

1. During monsoon, humidity is high. Increased moisture in air provides water required for rusting. Presence of oxygen completes the necessary conditions, increasing rate of corrosion.

2. Boiling removes dissolved oxygen from water. Covering with oil prevents oxygen from re-entering. Hence, one essential condition (oxygen) is absent.

3. a) Painting: Forms a protective layer preventing contact with air and moisture.
    b) Galvanization: Zinc coating prevents direct contact and offers better long-term protection.

Section C - Long Answer

(a) Painting provides temporary protection and needs regular maintenance. Galvanization coats iron with zinc, which prevents contact with air and moisture.

(b) Galvanized pipes are more durable because zinc coating provides long-lasting protection and resists corrosion better than paint.

(c) If ignored, rust weakens the pipe, causes leakage, contamination of water, and possible structural failure.