In order to complete another project, which is making iron tannate ink, I need a water-soluble salt of iron, and one of the best iron salts for this application is iron (II) sulfate (ferrous sulfate).
Rather than buying an entire pound of this salt, I wanted to make a small amount of ferrous sulfate to see if the reaction would even work. I then debated the best way to make this salt. The most obvious method would be to react iron metal with sulfuric acid, but I’d rather avoid handling any dangerous sulfuric acid.
My next thought was to use a double displacement reaction in order to produce an insoluble form of another cation while yielding my soluble ferrous sulfate — this would allow me to filter out the undesirable precipitate, leaving behind a relatively pure ferrous sulfate solution. The main issue I faced was that I only had access to three sulfates of other cations: cupric sulfate, magnesium sulfate, and calcium sulfate.
Calcium sulfate is insoluble, therefore it is useless in this instance, and I couldn’t think of any iron salts I could use to react with the other two compounds. Therefore, I was stuck, until I learned about a much simpler reaction, one that was a single displacement reaction.
I didn’t pay attention to the fact that iron is more reactive than copper on the reactivity series, which means that iron wants the sulfate anion more than copper does. This conveniently means that I only needed to pour a hot solution of cupric sulfate over high-surface-area iron and I would get ferrous sulfate and copper metal!
CuSO4 (aq) + Fe (s) -> FeSO4 (aq) + Cu (s)
Theoretically, the only remaining steps were to filter out the copper powder and to boil the water out of the ferrous sulfate solution. When I filtered out the copper, I was left with a nearly clear solution that was slightly aquamarine in color; this was my reasonably pure ferrous sulfate solution.
The issue was when I tried boiling the solution in a stainless steel container, as the solution appeared to react with the container, forming rust. I then tried to boil the solution in the same container, but this time, I used parchment paper to prevent it from reacting with the metal, however, the solution rusted anyway. I then filtered the solution again and allowed it to evaporate in hopes that the low temperature would prevent the solution from rusting, but when I went to retrieve the crystals, they were surrounded by a lot of rust.
So much of the ferrous sulfate had reacted with the oxygen in the air and formed rust that my yield was only about 50%. I did want a larger quantity of ferrous sulfate, so I purchased some, however, this was a great learning experience.
This experiment caused me to come to the realization that copper salts are a great asset for single displacement reactions as copper is one of the least reactive metals, yet many of its salts are water-soluble. This does mean that copper salts are very corrosive to metals, especially those that are highly reactive (i.e. iron, aluminum, magnesium).
What do you think about this experiment?
Onward American 