Synthesis database: Iron(III) oxide synthesis

Iron(III) oxide is one of the most well known compounds of iron. It is relatively simple to synthesize this compound.

For the synthesis, one must prepare one graphite electrode, and one iron electrode, sodium chloride, a few lab beakers or jars, and a source of a direct current.

First, to a relatively small amount of water, some sodium chloride is added. In this case, about 10 grams of sodium chloride was added to about 200 mL of water.

After that, both electrodes where submerged in the electrolyte - the iron anode was connected to the positive pole, and the graphite cathode was connected to the negative pole.

The anode reaction is shown by the following equation:

2Fe -> 2Fe³⁺ + 6 electrons

while on the cathode, hydrogen from water is reduced:

6H₂O + 6 electrons -> 3H₂ + 6OH^-

First, the hydrate is formed (FeO(OH)), which passes into the desired form (Fe₂O₃) upon heating.

The minimal duration of the electrolysis depends on the power source. It can last from a few hours to several days. In our case, the reaction lasted about 6 hours. The result was a dark orange colored electrolyte which was full of small particles of hydrated iron(III) oxide.

After the reaction is finished, the electrolyte was set aside for a few hours so that the mentioned particles could settle to the bottom.

Afterwards, by using a pipette, most of the solution above the precipitate was removed. The remaining solution, together with the precipitate, was poured on a plate which was placed in the oven at about 150°C.

After about one hour, most of the remaining water evaporated. Only relatively clean and dry iron(III) oxide remained. The mentioned compound was then scraped off the plate and stored in a small airtight container, in order to avoid contact with moisture.