Ferric Sulfate: Structure, Properties, Risks And Uses

The ferric sulfate, iron sulfate (III) , vitriol or copperas mars Mars, is an inorganic compound of formula Fe 2 (SO4) 3 . Each iron atom has three ionic bonds with sulfate.

Ferric sulfate is found in a wide variety of minerals, mainly in the minerals pyrite and marcasite, where ferrous sulfate is connected with ferrous oxide (Fe0).

Other minerals such as coquimbite, kornelite, and lausenite are sources of ferric sulfate nona, hepta, and pentahydrate. On the other hand, it can be found in minerals such as Mikasita, where it forms a mixture with aluminum (Ferric sulfate Formula, 2005-2017).

Ferric sulfate is mostly extracted from nature, however it can also be prepared by evaporation of ferric oxide and sulfuric acid. It is generally prepared by treating ferrous sulfate and an oxidizing agent with sulfuric acid at elevated temperatures as follows:

2FeSO 4 + H 2 SO 4 + H 2 O 2 → Fe 2 (SO 4 ) 3 + 2H 2 O

Ferric sulfate solutions are prepared by injecting chlorine gas into a ferrous sulfate solution.

In aqueous solution Fe 2 (SO 4 ) 3 dissociates into Fe 3+ (aq) and SO 4 2- (aq) ions . The sulfate ions will be solvated by hydrogen bonds with water and the iron ions will form the hexahydrate complex (III), [Fe (H2O) 6 ] 3+ (What happens to iron (III) sulfate (ferric sulfate) in aqueous solution) ?, 2015).

Physical and chemical properties

Ferric sulfate is a hygroscopic solid whose appearance and aroma can vary depending on the amount of water contained in the salt.

The most common forms in which iron (III) sulfate is found in nature are hydrated penta and none. In such a case, the crystals of this compound may be yellow in color. When it is in anhydrous form, it has a gray color (Ferric sulfate, 2016). 

appearance of iron III sulfate

Ferric sulfate molecules form rhombic or rhombohedral crystals. Its anhydrous form has a molecular weight of 399.858 g / mol, its hydrated penta and none form have a molecular weight of 489.960 g / mol and 562,000 g / mol respectively (Royal Society of Chemistry, 2015).

Its density is 3.097 g / ml (anhydrous) and its melting point is 480º C (anhydrous) and 175º C (nona hydrated). It is slightly soluble in water and alcohol, while very slightly soluble in acetone and ethyl acetate and insoluble in sulfuric acid (National Center for Biotechnology Information, SF).

Iron III sulfate is acidic, being corrosive to copper, copper alloys, mild steel and galvanized steel (FERRIC SULFATE, 2016).

Reactivity and hazards

Ferric sulfate is a stable non-flammable compound, however, when heated it emits toxic vapors of iron and sulfur oxides.

It is very dangerous in case of ingestion, contact with the skin and eyes (irritant) and inhalation. The substance is toxic to the lungs and mucous membranes, and repeated or prolonged exposure to the substance may cause damage to these organs.

In case of eye contact, contact lenses should be checked and removed. An eye ointment should not be used and medical attention should be sought.

In case of contact with the skin, it should be washed immediately with plenty of water in a gentle way and taking care not to use non-abrasive soap. Cover irritated skin with an emollient, if irritation persists seek medical attention.

If the contact with the skin is severe, it should be washed with a disinfectant soap and cover the contaminated skin with an antibacterial cream. Seek medical attention.

In case of inhalation, the victim should be allowed to rest in a well-ventilated area and seek immediate medical attention.

In case of ingestion, do not induce vomiting, but loosen tight clothing such as a shirt collar, tie or belt. If the victim is not breathing, mouth-to-mouth resuscitation should be performed. As in the previous cases, immediate medical attention should be sought.

This type of compound does not require a specific type of storage. Shelves or cabinets strong enough to support the weight of the chemical are used, ensuring that it is not necessary to strain to reach the materials, and that the shelves are not overloaded (Material Safety Data Sheet Ferric sulfate, 2013).


Ferric sulfate is used in industry, in water and wastewater treatment operations because of its ability as a flocculant and coagulant and to eliminate the odor of sulfur compounds.

Ferric sulfate is used as a solid separating agent and oxidizing agent. In addition, this salt is used in the pigment industry and in medicine, it can be used as an astringent and a styptic.

In the work of Ibricevic (2000), 70 exposed carious primary molar teeth were treated, without symptoms and without any sign of root resorption in children aged 3 to 6 years (main age: 4.3 years) treated with conventional pulpotomy.

They used a 15.5% ferric sulfate solution (applied for 15 seconds for 35 teeth) and formocresol solution (5-minute procedure of Buckley’s formula for the next 35 teeth) as pulpotomy agents.

In both groups, pulp stumps were covered with zinc oxide eugenol paste. The permanent restorations were stainless steel crowns. The clinical control was every three months and the radiographic follow-up was six and twenty months after treatment.

The results in this period revealed a 100% clinical success rate in both groups. The radiographic success rate was 97.2% in both groups, while in 2.8% the cases showed internal root resorption.

Ferric sulfate and jarosite have been detected by the two Martian Rovers Spirit and Opportunity. These substances are indicative of highly oxidizing conditions that prevail on the surface of Mars .


  1. Ferric sulfate. (2016). Retrieved from chemicalbook: chemicalbook.com.
  2. FERRIC SULFATE. (2016). Retrieved from cameochemicals: cameochemicals.noaa.gov.
  3. Ferric sulfate Formula. (2005-2017). Retrieved from softschools: softschools.com.
  4. Ibricevic H1, a.-JQ (2000). Ferric sulfate as pulpotomy agent in primary teeth: twenty month clinical follow-up. Clin Pediatr Dent 24 (4), 269-272. 
  5. Material Safety Data Sheet Ferric sulfate. (2013, May 21). Retrieved from sciencelab.
  6. National Center for Biotechnology Information. (SF). PubChem Compound Database; CID = 24826. Retrieved from PubChem.
  7. Royal Society of Chemistry. (2015). Iron (III) sulfate. Retrieved from chemspider.
  8. What happens to iron (III) sulfate (ferric sulfate) in aqueous solution? (2015, August 8). Retrieved from stackexchange: stackexchange.com.

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