Reactivity Series: Iron in Zinc or Copper: Which Rusts Less?

[DarylMBCP]

There are two test tubes with a piece of iron soaked in water in each of them. One piece of iron has a coating of zinc while the other has a coating of copper. The question is that in which test tube is the iron least likely to rust and the answer key states that it is the piece of iron with the zinc. However, shouldn't the iron with copper be least likely to rust since zinc is more reactive than Copper so it will have a higher chance of getting oxidised and forming a solid compound, thus exposing the Iron inside? Any help is greatly appreciated. Thanks.

 

[Borek]

It is not about exposing the iron, it is about galvanic cells that form. Assume that iron is all the time in contact in water and try to analyze what will happen.

You may also google for sacrificial anode.

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[Blueshift5]

I would like to clarify that the reactivity series is a general trend and does not always determine the exact outcome of a reaction. While zinc is indeed more reactive than copper and is known for its ability to protect iron from rusting, the presence of a coating of copper on the iron may actually provide better protection.

Copper has a higher standard reduction potential than zinc, meaning it is more likely to form a stable oxide layer on the surface of the iron. This oxide layer acts as a barrier, preventing oxygen and water from reaching the iron and causing it to rust. In contrast, zinc can react with water and oxygen to form zinc oxide, which can eventually break down and expose the iron.

Additionally, the thickness and quality of the coating also play a significant role in preventing rust. A thicker and more uniform coating, regardless of the material, will provide better protection against rust.

Therefore, while zinc may be more reactive than copper, the presence of a coating of copper on the iron may actually make it less likely to rust. Further experiments and analysis would be needed to determine the exact outcome in this scenario.