When iron (Fe) and copper sulphate (CuSO4) solution react, they undergo a single displacement reaction, also known as a substitution reaction, to form solid copper (Cu) and aqueous iron sulphate (FeSO4). The iron can be solid or aqueous but the copper sulphate must be aqueous in order to facilitate the reaction.
There are several physical indicators of the reaction between iron and CuSO4. Aqueous CuSO4 is a blue solution, and it will lose its color as it reacts with the iron to form FeSO4. Once the reaction is complete and there is no more CuSO4 present in the solution, it will appear completely colorless. The copper displaced by iron in the reaction is visible as a pink-brown precipitate that usually forms on the unreacted mass of solid iron left over.
The iron and copper ions in the reaction are positively charged cations, while the SO4 polyatomic ion is a negatively charged anion. The displacement reaction from CuSO4 to FeSO4 occurs because although both metals readily react with SO4 to form an ionic salt, iron has a lower electronegativity than copper and has a greater attraction to the oppositely charged SO4 ion. The likelihood for a metal to displace another in any displacement reaction is determined by the reactivity sequence.