Ferrous Sulfate(FeSO4) Properties(25 Facts You Should Know)

Iron is an essential element. Combining the ion with sulphate gives an interesting compound.

Iron(II) Sulphate(FeSO4) belongs to the class of salts having affinity towards water. It can be produced displacing the lesser reactive metal sulphates.In the olden days, FeSO4 was made into iron gall ink for painting and scribbling but can destroy the paper with time. Fe2+ mostly forms octahedral coloured complexes.

Let us cover this compound’s interesting properties and reactions in this article.

Ferrous Sulfate IUPAC Name

The IUPAC name of Ferrous Sulphate is Iron(II) Sulphate.

Ferrous Sulfate Chemical Formula

The chemical formula of Ferrous Sulphate is FeSO4, consisting of one iron atom, one sulphur atom and four oxygen atoms respectively.

Ferrous Sulfate CAS Number

The CAS Number of FeSO4 are of four types:

Type of SulphateCAS Number
CAS Number chart

Ferrous Sulfate ChemSpider ID

The ChemSpider IDs (free chemical structure database) of FeSO4 are different for different variants of the compound:

Type of SulphateCAS Number
ChemSpider Chart

Ferrous Sulfate Chemical Classification

  • FeSO4 is a widely used reagent that is classified as a range of hydrated salts, reducing agents and medical supplements.
  • It is nearly insoluble in most organic solvents, it is soluble in water.
  • It is also known in the olden days as Green Vitriol.

Ferrous Sulfate Molar Mass

The molar mass of only FeSO4 is around 136 g/mol but the monohydrate form has a mass of 151.908 g/mol.

Ferrous Sulfate Color

FeSO4 is generally observed with a range of colours, from bluish-green crystals to white solids.

Ferrous Sulfate Viscosity

The viscosity of FeSO4 has a strict range from 7.0 x 10^-3 Pa-s for 38.8 wt% at 285.15 K to 4.6 Pa-s for 58.2 wt% at 260.15 K.

Ferrous Sulfate Molar Density

The molar densities of FeSO4 compounds are given below:

CompoundMolar Density(mol/cm3)Normal Density(g/cm3)
Anhydrous FeSO40.02403.650
Monohydrate FeSO40.01763.000
Heptahydrate FeSO40.00681.895
Density Table

Ferrous Sulfate Melting Point

Melting point of FeSO4:

Type of SulphateMelting Point (in Kelvin)
Melting Point Table

Ferrous Sulfate Boiling Point

FeSO4 solution usually boils above 300 ºC (573 K).

Ferrous Sulfate State at Room Temperature

FeSO4 exists in diverse states as a result of hydrates, from colourless powdery solids to bluish-green crystals. The anhydrous form also appears to be slightly yellowish.

Ferrous Sulfate Covalent Bond

The molecule is made up of net two single covalent bonds and two double bonds between O atoms and S as shown in the diagram.

  • S-O bond length: 1.51 Å
  • S=O bond length: 1.47 Å
FeSO4 Structure

Ferrous Sulfate Covalent Radius

The covalent radius of FeSO4 is not detectable as a covalent radius is to be measured for a single atom.

Ferrous Sulfate Electronic Configurations

The electronic configuration is the general distribution of electrons around different atomic orbitals of an atom. Let us see the electronic configuration of Ferrous Sulphate.

  • Iron electronic configuration- [Ar18] 4s2 3d6.
  • Sulphur has the electronic configuration- [Ne10] 3s2 3p4.
  • Oxygen electronic configuration- [He2] 2s2 2p4

Ferrous Sulfate Oxidation State

Oxidation state information:

  • Each Oxygen atom in FeSO4 bear -2 oxidation, so, the net oxidation state is -8.
  • The central atom in FeSO4, Sulphur, bears an oxidation number of +6.
  • Iron in FeSO4 has an oxidation number of +2.

Ferrous Sulfate Acidity

FeSO4 can be dubbed as an acidic salt of a strong acid H2SO4 and basic oxide Fe(OH)2. A 10% solution of FeSO4 has approximately a pH of 3.7-3.8.

  • Fe(OH)2 + H2SO4 = FeSO4 + 2H2O

Is Ferrous Sulfate Odourless?

FeSO4 does not have a specific smell.

Is Ferrous Sulfate Paramagnetic?

The paramagnetic substances can attract magnetic field and contains unpaired electrons. Let us look at the paramagnetic property of FeSO4.

FeSO4 is paramagnetic in nature. It behaves as a ferromagnet in certain conditions.

Ferrous Sulfate Hydrates

FeSO4 mainly exists in a variety of hydrated forms of formula FeSO4⋅xH2O. However, all of them produce the same hexa-aqua octahedral complex Fe(H2O)62+ in water. They are:

Iron Hydrate FormulaHydrate NameNotes
FeSO4⋅H2OMonohydrateObtained from szomolnokite
FeSO4⋅4H2OTetrahydrateObtained from rozenite
FeSO4⋅5H2OPentahydrateObtained from siderotil
FeSO4⋅6H2OHexahydrateObtained from ferrohexahydrite
FeSO4⋅7H2OHeptahydrateObtained from melanterite
FeSO4 Hydrates

Ferrous Sulfate Crystal Structure

Due to various forms, the crystal structures are listed below:

  • Anhydrous FeSO4 crystal structure- Orthorhombic and Pearson Symbol- oP24
  • FeSO4. H2O crystal structure – Monoclinic and Pearson Symbol- mS36
  • FeSO4. 7H2O crystal structure – Monoclinic and Pearson Symbol- mP108

Ferrous Sulfate Polarity and Conductivity

  • FeSO4 is observed as a network solid with a slightly polar covalent bond character.
  • The Fe-O bonds in FeSO4 is conductive over a range of temperatures.

Ferrous Sulfate Reaction with Acid

A general scheme of reaction of FeSO4 with acids is the oxidation of Fe from +2 to +3 oxidation state.

  • This reaction forms Iron(III) Sulphate with water but it should be performed cautiously due to Hydrogen Peroxide being erupted in acidic conditions.
  • 2FeSO4 + HSO4 + H2O2 Fe2(SO4)3 + H2O
  • On reacting FeSO4 with nitric acid, Nitric Oxide is evolved and Iron(III) sulphate is formed.
  • 6FeSO4 + 3HSO4 + 2HNO3 3Fe2(SO4)3 + 4H2O + 2NO
  • Simple double displacement reaction with dilute hydrochloric acid: FeSO4 + 2HCl FeCl2 + H2SO4

Ferrous Sulfate Reaction with Base

In reaction with alkali metal hydroxides, a dirty green gelatinous precipitate of Fe(OH)2 is formed that even does not dissolve in excess of alkali. The FeSO4 should be freshly prepared else it may oxidise to Fe3+state.

  • FeSO4 + 2KOH Fe(OH)2 + K2SO4
  • FeSO4 + 2NaOH Fe(OH)2 + Na2SO4

Ferrous Sulfate Reaction with Oxide

FeSO4 is not that responsive in reactions with different oxides. However, anhydrous FeSO4 decomposes at high temperatures to give Fe2O3 along with SO2 and SO3.

Ferrous Sulfate Reaction with Metal

Following reduction potential series, Zn is more reactive than Fe, thereby, may displace Fe from its sulphate. It is a displacement reaction.

  • FeSO4 + Zn ZnSO4 + Fe


Ferrous Sulphate is an analytical reagent widely used as iron supplement for maintaining iron levels in the blood. It can reduce chlorine gas, an ability for which it can also be used to lower the pH of farmlands without many toxic effects. The properties explained are much more prevalent in hydrate forms.

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