How to prepare ferrous sulphate solution from ferrous sulphate?
Answers
Simply adding FeSO4 to water is not an appropriate way to make a solution of FeSO4. To prove this, do the following. Add FeSO4 to any volume of water and then add a small amount of KSCN. The solution will turn a reddish color, why? Because FeSO4 immediately begins to disproportionate by the following reaction.
3 Fe2+→ 2 Fe3+ + Fe(s)
Iron (III) reacts with the SCN- ion to make the FeSCN2+ complex ion which is red. As a consequence, it is well known that FeSO4 solutions are not stable. To help stabilize this solution we need to force the disproportionation reaction backwards towards the Fe2+ ion. To do this, solutions of FeSO4 are always made acidic by adding H2SO4 to them (about 3 M H2SO4 ) and a chunk of iron is added to help move the reaction towards the formation of FeSO4.
So, when we make FeSO4 solutions, they are acidified with H2SO4 and a chunk of iron is added to help stabilize the solution.