Question

Why does the color of sulphate solution change when an iron nail is dipped in it?

Answer 1

Answer: Displacement reaction occurs.

As iron is more reactive than copper, it displaces copper from the copper sulphate solution to form a green color Iron sulphate solution.

$\underset{Iron}{Fe\left(s\right)}+\underset{Coppersulphate\left(blue\right)}{CuS{O}_4\left(aq\right)}🡪\underset{Ironsulphate\left(green\right)}{FeS{O}_4\left(aq\right)}+\underset{Cpopper}{Cu\left(s\right)}$

WIn this way concentration of copper sulphate decreases while the concentration of ferrous sulphate increases.

Hence, the iron nail is dipped in copper sulphate solution the colour changes from blue to green.