Video: Metals Used as Sacrificial Coatings on Iron

Which of the following metals could be used as a sacrificial coating on iron to prevent rust formation? [A] Sn [B] Pt [C] Cu [D] Pb [E] Al

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Video Transcript

Which of the following metals could be used as a sacrificial coating on iron to prevent rust formation? (A) Sn, (B) Pt, (C) Cu, (D) pb, or (E) Al.

The answer options are tin, platinum, copper, lead, and aluminum. The question talks about a sacrificial coating on iron to prevent rust formation. When iron comes into contact with oxygen and water, it is converted or oxidized into iron oxide, which is rust. Rust is red-brown and flaky with little strength, so iron often needs to be coated to prevent it from rusting so that it can maintain its strength. We can use a metal reactivity series to choose which metal is suitable for a coating on iron.

The metals on this reactivity series are listed in order of increasing reactivity going from the bottom to the top. Potassium at the top is the most reactive metal. It loses electrons and is oxidized the most easily of all these metals. Platinum at the bottom of the list is the least reactive. It loses electrons or is oxidized the least easily. Platinum and gold are inert and unreactive under normal conditions. Under normal conditions, they are not oxidized. When a thin metal coating is placed on iron, oxygen and water are prevented from coming into contact with the surface of the iron and thus prevents it from rusting.

The metal coating should be made from a metal above iron in the reactivity series. Potassium, sodium, lithium, calcium, magnesium, aluminum, and zinc are all more reactive than iron. This means they will be oxidized more easily than iron, and it means that they can donate electrons to the iron preventing the iron from being oxidized itself. So even if some of the thin metal coating is accidentally scratched off the surface and even if the metal iron comes into contact with oxygen and water, it will not rust. Instead, the coating is oxidized. We say the coating is sacrificial. It sacrifices or gives its electrons to the iron, and in this way, the iron is protected although the coating itself is oxidized.

Of the possible answer options, only aluminum is higher than iron in the reactivity series. Tin, platinum, copper, and lead are all less reactive than iron and so cannot be sacrificial protectors of iron. So the metal which could be used as a sacrificial coating on iron to prevent rust formation is Al, aluminum.

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