sky-blue or green monoclinic crystals or crystalline powder
Ferrous sulfate heptahydrate
25.6 g/100 mL (20 °C) in water
Ferrous sulfate, commonly known as green vitriol, is a sulfate of iron consisting of sky-blue or green monoclinic crystals or crystalline powder, with a relative density of 1.8987 and melting point of 64 °C; it is odorless and convergent and weathers when exposed to air, with the surface turning into a white powder; it is subject to oxidization in moist air, with a brown ferric subsulfate appearing on the surface; it is water glycerol soluble and insoluble in alcohol; ferrous sulfate is reductive and turns from a heptahydrate into a tetrahydrate at 56.6°C, and into a monohydrate at 64.6°C; it loses six crystal water molecules at 90°C, and all the crystal water molecules at 300°C, and decomposes to give off SO2 and SO3 in red hot state; it is also corrosive and fluoresces in dry air; its anhydride form is a white powder, which turns blue-green when reacting with water.
Mainly used as a flocculant and has good flocculation and decolorization; it can also be used to remove heavy metal ions, oils, and phosphorus and for sterilization.