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 Sulphate	CAS Number
Anhydrous	7720-78-7
Monohydrate	17375-41-6
Heptahydrate	7782-63-0

Ferrous Sulfate ChemSpider ID

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

Type of Sulphate	CAS Number
Anhydrous	22804
Monohydrate	56459
Heptahydrate	22804

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:

Compound	Molar Density(mol/cm3)	Normal Density(g/cm3)
Anhydrous FeSO4	0.0240	3.650
Monohydrate FeSO4	0.0176	3.000
Heptahydrate FeSO4	0.0068	1.895

Ferrous Sulfate Melting Point

Melting point of FeSO₄:

Type of Sulphate	Melting Point (in Kelvin)
Anhydrous	953
Monohydrate	573
Heptahydrate	335

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

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 Formula	Hydrate Name	Notes
FeSO4⋅H2O	Monohydrate	Obtained from szomolnokite
FeSO4⋅4H2O	Tetrahydrate	Obtained from rozenite
FeSO4⋅5H2O	Pentahydrate	Obtained from siderotil
FeSO4⋅6H2O	Hexahydrate	Obtained from ferrohexahydrite
FeSO4⋅7H2O	Heptahydrate	Obtained from melanterite

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 + H_2­SO₄ + H₂O₂ → Fe₂(SO₄)₃ + H₂O
• On reacting FeSO₄ with nitric acid, Nitric Oxide is evolved and Iron(III) sulphate is formed.
• 6FeSO₄ + 3H_2­SO₄ + 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

Conclusion

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.