Corrosion Causes and Prevention - UNSOLVED PRACTICE SET

Q7. Define corrosion. Write the chemical equation for the rusting of iron. What are the necessary conditions for rusting?

Q8. List any four methods of preventing corrosion of iron. Explain the principle behind galvanization.

Q9. Your father paints the iron gate of your house every year before the monsoon. Explain why painting prevents rusting and why it needs to be done regularly.

Q10. Why does aluminium not corrode as severely as iron, even though aluminium is more reactive than iron? Explain the role of aluminium oxide.

Q11. What is the difference between rusting and tarnishing? Give one example of each.

Q12. Why are iron ships and bridges more prone to corrosion in coastal areas compared to dry inland areas? Explain.

Q13. Define corrosion and explain the process of rusting of iron with a chemical equation. What are the necessary conditions for rusting? Describe at least four methods of preventing corrosion and explain the scientific principle behind each method. Why is aluminium more resistant to corrosion than iron despite being more reactive?

Q14. A student performs experiments to study the conditions necessary for rusting:

Test tube A: Iron nails + dry air + calcium chloride (drying agent)

Test tube B: Iron nails + boiled water + oil layer (no air)

Test tube C: Iron nails + water + air

Test tube D: Iron nails + salt water + air

(a) Predict the observations in each test tube after one week.

(b) Which test tube(s) will show rusting? Explain why.

(c) Why is calcium chloride used in Test tube A?

(d) Why is boiled water used in Test tube B?

(e) What does Test tube D tell you about the effect of salt on rusting?

(f) Write the chemical equation for rusting.

Q15. "Corrosion is a silent thief that costs India billions of rupees every year, but it can be prevented with simple scientific understanding." Discuss this statement by explaining: (i) the economic impact of corrosion on Indian infrastructure like bridges, railways, and pipelines, (ii) why the Konkan Railway faces special corrosion challenges, (iii) how traditional methods like oiling and painting are still relevant, and (iv) modern methods like cathodic protection and protective coatings used in industry.

Q16. The Indian Railways maintains 68,000 km of track across the country.

(a) If 1 km of track contains 500 tonnes of iron, calculate the total iron in the railway network.

(b) If the annual corrosion rate is 0.5% in coastal areas and 0.2% in dry areas, and 30% of the track is in coastal areas, calculate the total iron lost to corrosion annually.

(c) If replacing corroded track costs ₹50,000 per tonne, calculate the annual economic loss due to corrosion.

(d) The Railways spends ₹100 crore annually on corrosion prevention (painting, greasing, etc.). Calculate the cost-benefit ratio if this prevents 80% of the potential corrosion loss.

(e) Why is the Konkan Railway particularly vulnerable to corrosion, and what special measures are taken?

Q17. A construction company builds a bridge using 1000 tonnes of structural steel.

(a) If the steel is painted with a protective coating that lasts 5 years, and unpainted steel corrodes at 1% per year, calculate the mass of steel saved over 20 years by painting.

(b) If painting costs ₹10,000 per tonne and replacement steel costs ₹50,000 per tonne, calculate the net savings over 20 years.

(c) The company considers galvanizing instead of painting. If galvanizing costs ₹15,000 per tonne but lasts 15 years, calculate the long-term cost-effectiveness.

(d) Why is galvanization more effective than painting for bridges in coastal Maharashtra?

(e) If the bridge is in a polluted industrial area where acid rain accelerates corrosion by 50%, how does this affect the choice of protection method?

Q18. A car manufacturer in India wants to improve the corrosion resistance of its vehicles.

(a) The car body is made of steel. If a car body contains 300 kg of steel and the manufacturer applies a zinc coating (galvanization) of 3% by mass, calculate the mass of zinc used per car.

(b) If the manufacturer produces 100,000 cars per year, calculate the annual zinc requirement.

(c) Zinc is more reactive than iron. Explain how the zinc coating protects the steel even if it is scratched.

(d) Some luxury cars use stainless steel (an alloy of iron with chromium and nickel). If stainless steel contains 18% chromium and 8% nickel, calculate the mass of each metal in a 300 kg car body.

(e) Why is stainless steel more expensive than galvanized steel, and why is it preferred for high-end applications?

(f) If the manufacturer switches from painting to powder coating, which reduces corrosion by 90% compared to painting's 70%, calculate the additional steel saved per car over 10 years (assuming 0.5% annual corrosion rate for unprotected steel).