Question

An iron nail was immersed in a solution of copper sulfate and when it was removed from the solution, it was coated with a layer of copper metal. Hereafter, a different iron nail was immersed in a solution of zinc nitrate and removed this nail rusted?(con)

just as rapidly as a new iron nail. Rank these three metals in order of activity from most active to least active.

a). Fe>Cu>Zn
b). Zn>Fe>Cu
c). Cu>Fe>Zn
d). Zn>Cu>Fe

Answer 1

b) `"Zn" > "Fe" > "Cu"`

Explanation:

Reactive metals displace unreactive metal ions from their solutions.

Iron in the first nail was capable of reducing and displacing copper ions in the `"Cu" "SO"_4` solution indicating that `"Fe"` is more reactive than `"Cu"`.

`ul("Fe" (s)) + "CuSO"_4 to ul("Cu"(s)) + "FeSO"_4(aq)`

What's going on with the second nail might not be as evident as the first one. Let's start with an assumption: assuming that iron `"Fe"` is more reactive than zinc such that it is capable of replacing zinc `"Zn"` from its solution.

Immersing the iron nail in the `"Zn"("NO"_3)_2` solution will coat it with a layer of metallic zinc. Coating iron, a metal that rusts- or gets oxidized- rapidly in humid air, with a layer of less reactive metal would hinder its oxidation. By this assumption, coating zinc would make the iron nail not as suspectable to rusting as a nail with no coating. However, the observation that the two nails rust at the same rate disagrees with the assumption meaning that iron is less reactive than zinc. Thus

`"Zn">"Fe"`

Also,

`"Fe">"Cu"`

therefore

`"Zn">"Fe">"Cu"`