Question

Which of the following statements is not correct about rusting of iron?

• A. Coating of iron surface by tin prevents rusting, even if the tin coating is peeling off.
• B. When pH lies above 9 or 10, rusting of iron does not take place.
• C. Dissolved acidic oxides SO₂, NO₂
• D. Rusting of iron is envisaged as setting up of electrochemical cell on the surface of iron object.

Answer 1

The Correct Option is A

To determine which statement is not correct about the rusting of iron, let's examine each of the given options:

1. Coating of iron surface by tin prevents rusting, even if the tin coating is peeling off: 

This statement is incorrect. When the tin coating is intact, it protects iron by preventing exposure to air and water. However, if the tin coating peels off, iron becomes exposed. Tin is less reactive compared to iron, and once exposed, iron can react with water and oxygen, accelerating the rusting process beneath the peeled sections. Thus, the tin coating offers no protection when it is peeling off.

1. When pH lies above 9 or 10, rusting of iron does not take place:

This statement is correct. At high pH levels, the concentration of hydroxide ions (OH⁻) is high, which inhibits the rusting process by forming protective layers on the iron surface, thus preventing corrosion.

1. Dissolved acidic oxides SO₂, NO₂ in water act as a catalyst in the process of rusting:

This statement is correct. These oxides, when dissolved in water, form acidic solutions that can enhance the electrochemical reactions involved in the rusting process, effectively acting as catalysts.

1. Rusting of iron is envisaged as setting up of electrochemical cell on the surface of iron object:

This statement is correct. Rusting of iron involves electrochemical reactions where iron acts as an anode and air/water act as a cathode, forming an electrochemical cell that facilitates the oxidation of iron.

The incorrect statement is the first one: "Coating of iron surface by tin prevents rusting, even if the tin coating is peeling off."

Answer 2

When the tin coating is peeled off, the iron is exposed and rusts more quickly due to galvanic action, making Option (1) incorrect. Tin itself does not prevent rusting once it is removed.

The Correct answer is: Coating of iron surface by tin prevents rusting, even if the tin coating is peeling off.