What happens when iron sulfate is heated

Ferrous sulfate FeSO 
White dust

Light green prisms
Mineral melanterite
in coatings on pebbles
molar mass 151.908 g / mol
(Heptahydrate 278.014 g / mol)
AGW not specified
density 3.65 g / cm3    
(Heptahydrate 1.895 g / cm3)   
decomposition +400 ° C
Water solubility(Heptahydrate)
100g H2O dissolve 26.58 g at 20 ° C
GHS 07
Hazard classes + category  
Acute toxicity oral 4
Eye irritation 2
Skin irritation 2
HP rates (see note)      
H 302, 315, 319 P 280.1-3, 301 + 312, 302 + 352, 332 + 313, 305 + 351 + 338, 337 + 313
disposal G 4
print a labelGerman nameEnglish name
CAS 7720-78-7 
CAS 7782-63-0
Ferrous sulfate
Iron (II) sulfate heptahydrate *
Iron (II) sulfate
Iron (II) sulfate heptahydrate
*) Preferred for school, the bottle shown shows the heptahydrate.
Iron (II) sulfate heptahydrate was earlier under the German name Iron vitriol known. It forms light blue or light green crystals. It is commercially available as a green, crystalline powder. The crystals are light blue in their very pure form, but they are colored green even by minimal impurities with iron (III) salts.

Crystallized iron (II) sulfate heptahydrate
after extraction from iron and sulfuric acid.

Iron (II) sulfate is readily soluble in water and in ethylene glycol. When heated, the water solubility increases. It does not dissolve in ethyl alcohol and acetone. In a saturated solution, the tetrahydrate forms at 56.6 ° C, and the monohydrate forms at 65 ° C, which is retained even after further heating. After the previously heated water has evaporated from the solution, the monohydrate is obtained as a white powder which decomposes above 400 ° C. with elimination of sulfur dioxide. When heated dry you first get the white monohydrate and then various colored oxidation products that can be used as iron oxide pigments.


When iron (II) sulfate is heated, colored iron oxides or iron hydroxides are produced.
It is made by dissolving and boiling iron or iron waste in excess in 20% sulfuric acid. In addition to iron sulfate, hydrogen is also produced:
Fe + H2SO4  FeSO4 + H2    
The product is filtered into a dish and diluted with water only after the reaction has ended. The iron (II) sulfate heptahydrate crystallizes out of the cold solution in crystals.


Iron (II) sulphate is an important intermediate product in the production of other iron compounds; iron (III) oxide, for example, is formed during annealing. It is also used in the manufacture of iron gall inks, in medicine for iron preparations, in veterinary medicine as a hemostatic agent for foot and mouth disease, for preserving wood, for the production of iron oxide pigments, as a flocculant in wastewater treatment, as a catalyst in ammonia synthesis and in analytical applications Chemistry for the detection of nitrites and nitrates.