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

Jun 11, 2018

b) $\text{Zn" > "Fe" > "Cu}$

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 ${\text{Cu" "SO}}_{4}$ solution indicating that $\text{Fe}$ is more reactive than $\text{Cu}$.

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 $\text{Fe}$ is more reactive than zinc such that it is capable of replacing zinc $\text{Zn}$ 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

$\text{Zn">"Fe}$

Also,

$\text{Fe">"Cu}$

therefore

$\text{Zn">"Fe">"Cu}$