What is Ferrous Sulfate?

Ferrous sulfate, also known as Iron(II) sulfate represents a spectrum of salts having the formula of FeSO4.xH2O. Earlier, it was also known as the green vitriol of copperas. It was formerly used as a fixative for dyes in textile industries, blackening hide and as a component in ink. Approximately 7 centuries ago, the process of preparing sulfuric acid included the distillation of ferrous sulfate. 

Iron(II) sulfate is a bluish-green chemical that is employed in several applications like manufacturing ink, dye, and medicines. Some popularly known mineral forms of ferrous sulfate are Melanterite FeSO4·7H2O (blue-green), Rozenite FeSO4·4H2O (white, maybe a dehydrated version of melanterite).

Some of its mineral forms that are moderately rare are Ferrohexahydrite (FeSO4·6H2O), Siderotil (FeSO4·5H2O), Szomolnokite (FeSOH2O).

Ferrous Sulfate Structure – FeSO4

Iron(II) Sulfate or Ferrous sulfate denotes a range of salt. The formula is salt is FeSO4.xH2O. Heptahydrates are the most common form of salt. The hydrated salt is used medically for treating iron deficiency. It can also be used for various industrial applications as well. The Iron(II) sulfates dissolve in water to give the same aqua complex. This aqua complex has octahedral geometry. The formula of the aqua complex is [Fe(H2O)6]2+. It is paramagnetic. 

Physical Properties of Ferrous Sulfate- FeSO4

  • Chemical formula- FeSO4

  • Molar mass- 

    • Anhydrous ferrous sulfate- 151.91 g/mol

    • Monohydrate ferrous sulfate- 169.93 g/mol

    • Pentahydrate ferrous sulfate- 241.99 g/mol

    • Hexahydrate ferrous sulfate- 260.00 g/mol

    • Heptahydrate ferrous sulfate- 278.02 g/mol

  • Colour

    • Anhydrous- White crystals

    • Monohydrate- Yellowish white crystals

    • Heptahydrate- Bluish-green crystals.

  • Melting point- 56-64°C

  • Boiling point- >300°C

  • Solubility in alcohol- Negligible

  • Solubility in water- 

    • Monohydrate- 44.69 g/100mol at 77°C

    • Heptahydrate- 15.65 g/100mol at 0°C, 20.5 g/100mol at 10°C.

  • Refractive index- 

    • Monohydrate- 1.591

    • Tetra hydrates 1.526-1.528

    • Pentahydrate- 1.513-1.515

    • Hexahydrate- 1.468

    • Heptahydrate- 1.471

Chemical Properties of Ferrous Sulfate


In the manufacture of steel, the steel product is put through baths of sulfuric acid before coating or plating. This procedure yields large amounts of ferrous sulfate as a byproduct.

Fe + H2SO4 → FeSO4 + H2

Also, huge quantities can be obtained from the process of producing titanium dioxide from titanium-iron oxide minerals through the sulfate process.

Ferrous sulfate can be commercially prepared by oxidation of pyrite. In this reaction, ferrous sulfate is formed along with sulphuric acid. 

Ferrous sulfate can also be obtained by displacement of metals less reactive than Iron from their sulfates: 

CuSO4 + Fe → FeSO4 + Cu


If ferrous sulfate is dissolved in water, it forms the metal aquo complex [Fe(H2O)6]2+ It is a nearly colourless and paramagnetic ion.

On heating, ferrous sulfate initially loses its water of crystallization, then the actual green crystals are transformed into an anhydrous solid of white-colour. If it is further heated, then the anhydrous solid discharges white fumes of sulfur trioxide and sulfur dioxide leaving behind reddish-brown coloured ferric oxide. Ferrous sulfate begins to decompose at nearly 680 °C (1,256 °F).

2 FeSO4 → Fe2O3 + SO2 + SO3

Like all other ferrous salts, ferrous sulfate is a reducing agent. For instance, it reduces nitric acid to nitrogen monoxide and chlorine to chloride:

FeSO4 +  HNO3   H2SO4 →  Fe2(SO4)3 +  H2O +  NO

FeSO4 +  Cl2 →  Fe2(SO4)3 +  FeCl3

Uses of Ferrous Sulfate

In industries, ferrous sulfate is primarily used as an antecedent to other iron constituents. It acts as a reducing agent. In earlier times, it was used as dye fixative in textile industries. It was also used for blackening hide and a component of ink.

  1. Medical Use - Ferrous sulfate is utilized to enhance food items for treating and avoiding anaemia that is caused by iron deficiency.

  2. Colourant - Ferrous sulfate was employed for manufacturing inks. It is also used for dyeing wool as a mordant. Harewood, a material used in marquetry and parquetry since the seventeenth century, is also made utilizing ferrous sulfate.

Occasionally, it is used as an artificial colourant in canned black olives. Ferrous sulfate is also used to stain concrete and sandstones and limestones a yellowish rust colour. Ferrous sulfate solutions are used in the woodwork to colour maple wood with a silvery hue.

  1. Plant Growth - Ferrous sulfate is utilized as a soil modification to lower the pH of the soil so that the soil's nutrients are easily accessible to the plants.

In horticulture, it is used to treat iron chlorosis. It is also used as a moss killer and a lawn conditioner.

  1. Other Uses - 

  • Used to precipitate metallic gold from a solution of gold and aqua regia.

  • Used to purify water and to prevent eutrophication.

  • Used to identify mushrooms.

  • Used as an iron catalyst constituent in Fenton's reagent.

  • Used as a major constituent in manufacturing ink.

FAQs (Frequently Asked Questions)

1. What are the benefits of ferrous sulfate? How are ferrous metals advantageous?

Ferrous sulfate has a major role to play in the biological world. This mineral plays a vital role in our body. It is used to treat and prevent anaemia that is caused due to iron deficiency, meaning a shortage of RBCs (red blood corpuscles) that is, lack of iron in the body.

Ferrous sulfate is lighter yet has powerful tensile strength. Some of the benefits of ferrous sulfate are high current conductivity (found in copper), zinc that is resistant to corrosion, and tolerance to magnetic force. These ferrous metals are modified into either intermediate metals or finished products.

2. What is the main difference between ferrous and ferric?

Iron can have numerous valencies. It is determined as ferric or ferrous depending on the number of electrons it loses. When an iron atom loses 3 electrons, it obtains a +3 charge and serves as a ferric ion (Fe+3). When an iron atom loses 2 electrons, it obtains a +2 charge and serves as a ferrous ion (Fe+2). The electronic configuration ferrous ion is 3s2 3p6 3d6 and the electronic configuration of ferric ion is 3s2 3p6 3d5. According to Hund's rule of multiplicity, ferric ions are more stable than ferrous ions because it is half-filled. Example of ferrous compounds: FeO. Example of ferric compounds: FeCl3.