Which of the following statements is not correct about rusting of iron?
Coating of iron surface by tin prevents rusting, even if the tin coating is peeled off.
When pH lies above or , rusting of iron does not take place.
Dissolved acidic oxides , in water act as catalysts in the process of rusting.
Rusting of iron is envisaged as setting up of electrochemical cell on the surface of iron object.
Correct answer:A
Standard Method
Given: Four statements about rusting of iron are to be checked.
Find: The statement which is not correct.
The solution states that the correct option is A. It explains that tin protects iron only as long as the tin coating remains intact. If the tin coating is peeled off, the exposed iron comes in contact with air and moisture.
Since tin is less reactive than iron, exposure of iron in contact with tin can accelerate corrosion of the iron due to galvanic action. Therefore, the statement saying that tin coating prevents rusting even if the coating is peeled off is incorrect.
The remaining statements are treated as correct in the solution:
Therefore, the incorrect statement is Option A.
Elimination Idea
Given: A conceptual question on rusting of iron.
Find: The statement that is not correct.
Focus on the statement involving tin coating. A protective coating works only while it remains continuous. Once the coating is peeled off, iron gets exposed.
Also, because tin is nobler than iron, the exposed iron can corrode faster near the damaged region. Hence the claim that rusting is prevented even if tin coating is peeled off cannot be true.
So, the correct choice is A.
Assuming every metal coating protects iron even after the coating is damaged. This is wrong because protection depends on the nature of the coating metal and whether the layer is intact. For tin-coated iron, peeling can expose iron and promote corrosion.
Confusing tin coating with zinc galvanization. This is wrong because zinc is more reactive and can offer sacrificial protection, whereas tin is less reactive than iron. Do not treat both coatings the same way.
Thinking rusting is only a direct reaction with oxygen. This is incomplete because rusting is an electrochemical process with anodic and cathodic regions on the iron surface. Use the electrochemical model to judge such statements.
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