Question

The colour of the solution observed after about 1 hour of placing iron nails in copper sulphate solution is:

• A. Blue
• B. Pale green
• C. Yellow
• D. Reddish brown

Hint:

In displacement reactions, a more reactive metal (iron) displaces a less reactive metal (copper) from its solution. This results in the formation of solid copper and a colour change.

Answer 1

The Correct Option is D

When iron nails are placed in copper sulphate solution, a displacement reaction takes place. In this reaction, iron (Fe) displaces copper (Cu) from its salt \((CuSO_4)\) because iron is more reactive than copper. The reaction is: \[ \text{Fe} (s) + \text{CuSO}_4 (aq) \rightarrow \text{FeSO}_4 (aq) + \text{Cu} (s) \] In this process, copper metal is displaced from the solution, and it starts appearing as reddish-brown solid at the bottom of the container, while iron ions enter the solution to form iron(II) sulphate. The colour change is a direct result of the copper metal (reddish-brown) formed in the solution. Thus, the correct answer is (D) Reddish brown.