Question

Why does the iron nail become brownish when dipped in copper sulfate solution?

• A. Copper gets deposited on the nail
• B. Iron reacts with oxygen
• C. The nail rusts
• D. The nail undergoes thermal decomposition

Hint:

This is a classic example of a metal displacement reaction. Remember that the more reactive metal always displaces the less reactive metal from its salt solution.

Answer 1

The Correct Option is A

Step 1: Recall the reactivity series of metals.
As established earlier, the reactivity series ranks metals in order of their chemical reactivity. Iron (Fe) is placed above copper (Cu) in the reactivity series, indicating that iron is more reactive than copper.
Step 2: Predict the reaction between iron and copper sulfate solution.
When a more reactive metal (iron) is placed in a solution of a salt of a less reactive metal (copper sulfate, \(CuSO_4\)), a displacement reaction occurs. The more reactive metal displaces the less reactive metal from its salt solution. In this case, iron will displace copper from copper sulfate solution. The balanced chemical equation for this reaction is: \[ Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s) \]
Step 3: Observe the products of the reaction.
The products of this reaction are iron (II) sulfate (\(FeSO_4\)) solution, which is typically light green, and solid copper (\(Cu\)), which is reddish-brown in colour.
Step 4: Explain the brownish appearance of the iron nail.
As the reaction proceeds, metallic copper is deposited on the surface of the iron nail. This deposited copper is brownish in colour, causing the iron nail to take on a brownish appearance.
Step 5: Analyze the other options.

1. 
   Copper gets deposited on the nail:
   This is correct, as explained by the displacement reaction.
2. 
   Iron reacts with oxygen:
   This would occur if the iron nail were exposed to air and moisture, leading to rusting (formation of iron oxides), which is typically reddish-brown. However, the question specifies dipping in copper sulfate solution, so the primary reaction is with copper sulfate, not directly with atmospheric oxygen.
3. 
   The nail rusts:
   Rusting is the corrosion of iron, primarily involving reaction with oxygen and water. While the nail might eventually rust if left exposed after the experiment, the immediate brownish coating upon dipping in copper sulfate solution is due to copper deposition.
4. 
   The nail undergoes thermal decomposition:
   Thermal decomposition involves breaking down a substance by heating it to a high temperature. This is not relevant to dipping an iron nail in copper sulfate solution at room temperature.

Therefore, the iron nail becomes brownish when dipped in copper sulfate solution because copper gets deposited on the nail due to a displacement reaction.