What is Iron (II) Sulphate heptahydrate and what is it used for ?

What is Iron (II) sulphate Heptahydrate

Iron (II) sulphate heptahydrate also known as Ferrous (II) Sulphate is a blue green crystal with the formula FeSO4.7H2O. Originally it was known as “green vitriol” or “copperas”. It is soluble in water and melts at 64C. It is produced as a by-product of the pickling of steel. It is used as a mordant in dyeing wool, in the manufacture of ink, in water purification as a substitute for aluminum sulphate, as a fertilizer, and as a feed additive. It is also used to produce magnetic ferric oxide.


  • Synonyms: Ferrous sulfate; Iron (ii) sulfate; green vitriol; iron vitriol; copperas;
  • Appearance: blue/green crystals
  • CAS No: 7782–63–0
  • EINECS No: 231–753–5
  • FeSO4.7H2O: > 99%
  • Molecular weight: 278.01
  • Fe: 20% min
  • Pb: 0.002% max
  • Solubility: Soluble in Water 486g/L
  • Insoluble in: Alcohol
  • Melting Point: 64C
  • Boiling Point: 400C decomposes


  • It is used as a lawn conditioner,and moss killer. See below for full details on application.
  • Industrially, ferrous sulfate is mainly used as a precursor to other iron compounds.
  • It is a reducing agent, mostly for the reduction of chromate in cement.
  • Used in the manufacture of inks including iron gall ink.
  • It is used a mordant for wool dyeing.
  • Ferrous sulphate can also be used to stain concrete and some limestones and sandstones a yellowish rust color.
  • Woodworkers use ferrous sulfate solutions to color maple wood a silvery hue.

In horticulture it is used for treating iron chlorosis (yellowing of folliage caused by iron deficiency). Although not as rapid-acting as iron chelate, its effects are longer-lasting. It can be mixed with compost and dug into to the soil to create a store which can last for years. Ferrous sulfate is sometimes added to the cooling water flowing through the brass tubes of a turbine condenser. It forms a corrosion-resistant, protective coating on the inside of the tube.

It has been applied for the purification of water by flocculation and for phosphate removal in municipal and industrial sewage treatment plants to prevent eutrophication of surface water bodies.

It is used as a traditional method of treating wood panel on houses, either alone dissolved in water or as a component of water-based paint.

Application Rates for Moss Killing

As regards the rates of application for the above material, this very much depends on the end use of the material and also the location where the product is to be used. What has to be stressed is that no two sets of circumstances will be the same and therefore a small area would need to be tested to satisfy yourself of suitability

For use as a Moss Killer

We would advise that initially you test a small area with a 1% Ferrous Sulphate Heptahydrate solution (ie. 10gms/1L of water). If this does not give the desired effect a stronger solution can be used up to a maximum of 5% Ferrous Sulphate Heptahydrate (50gms/1L of water ).

A typical average strength to use would be a 3% solution. To make the solution add 30g of ferrous sulphate for every litre of water (for example for a 15L sprayer you will need 450g of ferrous sulphate).

How much Iron sulphate is needed to treat 1 acre

An acre is approx 4050 sq m. Therefore a 3% solution applied at 5sq m per litre will require 810L of solution which equates to 24.3kg of ferrous sulphate powder.

Application of the solution should be at a rate of 5 square metres for every litre of chemical mix. Apply evenly over lawn etc avoiding overspray contact with other plants and paths, patios etc.

After 2 to 3 days you will see that the moss has turned black in colour indicating that the moss has been successsfully killed. At this point one should use a tined rake to loosen and remove dead moss. Application of a lawnmower set to low cut will help in the removal. Please note: the grass cuttings and dead moss should not be added to compost bins.

Please be aware that ferrous sulphate is only for use on grass areas and is not designed to be used on hard surfaces as it may stain. For hard surfaces like roofs, paths, patios etc Zinc Sulphate can be used or a proprietry chemical like MossKill Premium.

If ferrous sulphate comes in contact with concrete for example it will stain the surface brown which effectively is a rust stain. To remove this stain one will need to use an acid solution like Oxalic acid (used as a 5% solution).

When treating lawns etc with ferrous sulphate keep pets off the surface for at least one week. This protects their well being and prevents transfer of residues onto hard surfaces (i.e. brown staining).

For application on agricultural pasture land / paddocks etc use at the same rates as above. Animals like horses must be kept of grasslands for at least 4 weeks before being allowed back to graze.

An over usage of Ferrous Sulphate can be harmful if the land being applied to has a low pH (very Acidic) as Ferrous Sulphate is naturally very acidic with a pH of 2.5.

NOTE: We must stress that this information can only be used as a guideline and is given in good faith. We cannot be held responsible for any adverse effects that may be experienced as a result of use of the above product.

Health & Safety

R-Phrases: R22 Harmful if swallowed. R36/38 Irritating to eyes and skin.

S-Phrases: S46 If swallowed, seek medical advice immediately and show container or label.

For full MSDS for iron sulphate / ferrous sulphate see website – click on link below.

Where to buy Buy Iron sulphate / Ferrous sulphate online


About mistralhowto

formulation chemist

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