Understanding the Iron Nail Copper Sulphate Reaction

When an iron nail is dipped in a copper sulphate solution, a chemical reaction occurs. You observe that the iron nail gets a brown coating, and the blue colour of the copper sulphate solution fades and turns greenish.

This change happens because iron is more reactive than copper. According to the reactivity series of metals, a more reactive metal can displace a less reactive metal from its salt solution.

The Chemical Reaction: Iron and Copper Sulphate

The reaction that takes place is between iron (Fe) metal and copper sulphate (CuSO\(_4\)) solution. The balanced chemical equation for this reaction is:

\(\text{Fe(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{FeSO}_4\text{(aq)} + \text{Cu(s)}\)

In this reaction:

• Iron metal (Fe) reacts with copper sulphate solution (CuSO\(_4\)).
• Iron displaces copper from copper sulphate.
• Iron sulphate (FeSO\(_4\)) is formed in the solution (which is green).
• Copper metal (Cu) is deposited on the iron nail (which is brown).

Why it is a Displacement Reaction

A displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. In this case, iron (Fe) is more reactive than copper (Cu), so iron displaces copper from the copper sulphate (CuSO\(_4\)) solution.

The brown coating on the iron nail is the displaced copper metal. The change in the colour of the solution from blue (copper sulphate) to green (iron sulphate) further confirms the reaction.

Analyzing Other Options

• Addition reaction: Involves two or more reactants combining to form a single product. This is not the case here, as we have two reactants forming two products.
• Decomposition reaction: Involves a single reactant breaking down into two or more simpler substances. This is not the case here, as we have two reactants.
• Substitution reaction: While related to displacement as one atom/group replaces another, the term 'displacement reaction' is more specific and commonly used for the type of reaction between a metal and a metal salt solution based on reactivity.

Therefore, based on the definition and the observed changes, the reaction between iron and copper sulphate is a displacement reaction.

Revision Table: Iron Nail Reaction

Additional Information on Reactivity Series and Displacement

The reactivity series of metals lists metals in order of their decreasing reactivity. A metal higher up in the series can displace a metal lower down from its salt solution or oxide.

Common Reactivity Series (excerpt):

K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au

Since iron (Fe) is placed above copper (Cu) in the reactivity series, iron is more reactive than copper. This higher reactivity allows iron to displace copper ions (Cu\(^{2+}\)) from the copper sulphate solution, forming iron(II) sulphate and solid copper metal.

This type of reaction is a classic example used to illustrate the concept of single displacement reactions, where one element displaces another from a compound.