Question

Why does iron displace copper from its salt solution?

Answer 1

The chemical element iron has the atomic number $26$, and it is represented as $Fe$. The chemical element copper has the atomic number $29$, and it is represented as $Cu$.

Complete answer:
Let us first understand a displacement reaction.
In a molecule, a displacement reaction occurs when an atom or a group of atoms is replaced by another atom. For example, when iron is added to a copper sulphate solution, the copper metal is displaced.
$A + B - C \to A - C + B$
The above equation is true only if $A$ is more reactive as compared to $B$.
Also, $A$ and $B$ have to be either:
Halogens where $C$ indicates a cation.
Different metals wherein $C$ indicates an anion.
Now, let us understand the reaction of iron displacing copper from its salt solution.
When iron nails are immersed in copper sulphate, iron displaces copper from copper sulphate, resulting in ferrous sulphate. Iron displaces copper as iron is more reactive as compared to copper. The copper metal deposits a brownish-red powder on the iron nails.
The reaction is as follows: $Fe\left( s \right) + CuS{O_4}\left( {aq} \right) \to FeS{O_4}\left( {aq} \right) + Cu\left( s \right)$
A chemical displacement reaction occurs when metallic iron displaces the copper ion $\left( {C{u^{2 + }}} \right)$ from its salt. The cupric ion is converted to metallic copper, and metallic iron is converted to ferrous iron.
The reaction is as follows: $Fe\left( s \right) + C{u^{2 + }}\left( {aq} \right) \to F{e^{2 + }}\left( {aq} \right) + Cu\left( s \right)$
Therefore, iron is more reactive as compared to copper. Hence iron can displace the copper from its salt solution.

Note:
A metal in the activity series can displace any metal in the series below it from its compound. The activity series is a collection of metals arranged in decreasing order of reactivity. The series has potassium at the top and gold at the bottom.