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Potassium ferrate

Potassium ferrate
IUPAC name Potassium ferrate(VI)
Other names Potassium ferrate
Dipotassium ferrate
Molecular formula K2FeO4
Molar mass 198.0392 g/mol
Appearance Dark purple solid
Density 2.829 g/cm3, solid
Melting point

>198 °C (decomposition temp)

Solubility in water soluble in 1M KOH
Solubility in other solvents reacts with most solvents
Crystal structure K2SO4 motif
Dipole moment 0 D
Main hazards oxidizer
R-phrases 8
S-phrases 17-36
Flash point non-combustible
Related Compounds
Other anions K2MnO4
Other cations BaFeO4
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Potassium ferrate is the chemical compound with the formula K2FeO4. This purple, paramagnetic salt is a rare example of an Fe(VI) compound. In most of its compounds, iron has the oxidation state II (i.e., Fe2+) or III (Fe3+). Reflecting its high oxidation state, FeO42- is a powerful oxidant. K2FeO4 has attracted interest for applications in "Green Chemistry" because the by-products of its use, iron oxides, are environmentally innocuous. In contrast, some related oxidants such as chromate are considered environmentally hazardous. The main difficulty with the use of K2FeO4 is that it is often too reactive, as indicated by the fact that it decomposes in water.[1]

Redox properties and applications

As a dry solid, K2FeO4 is stable. It decomposes with evolution of O2 in neutral and especially rapidly in acidic water. At high pH, aqueous solutions are stable. The deep purple solutions are similar in appearance to potassium permanganate. K2FeO4 is a stronger oxidizing agent than KMnO4.

Because the side products of its redox reactions are rust-like iron oxides, K2FeO4 has been described as a "green oxidant." Indeed it has been employed for waste-water treatment as an oxidant for organic contaminants and as a biocide. Conveniently, the reduced iron(III) oxyhydroxide is an excellent flocculant.

In organic synthesis, K2FeO4 oxidizes primary alcohols.[2]

It has also attracted attention as a potential cathode material in a "Super iron battery."

Synthesis and structure

Georg Ernst Stahl (1660 – 1734) first discovered that the residue formed by igniting a mixture of potassium nitrate (saltpetre) and iron powder dissolved in water to give a purple solution. Edmond Frémy (1814 – 1894) later discovered that fusion of potassium hydroxide and iron(III) oxide in air produced the compound produced was soluble in water corresponding to the composition of potassium manganate. In the laboratory, K2FeO4 is prepared by oxidizing an alkaline solution of an iron(III) salt with concentrated chlorine bleach.[3]

The salt is isostructural with K2MnO4, K2SO4, and K2CrO4. The solid consists of K+ and the tetrahedral FeO42- anion, with Fe-O distances of 1.66 Å.[4] The poorly soluble barium salt, BaFeO4, is also known.


  1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  2. ^ Green, J. R. “Potassium Ferrate” Encyclopedia of Reagents for Organic Synthesis 2001, John Wiley. doi:10.1002/047084289X.rp212.
  3. ^ Schreyer, J. M.; Thompson, G. W.; Ockerman, L. T. "Potassium Ferrate(VI)" Inorganic Syntheses, 1953 volume IV, pages 164-168.
  4. ^ Hoppe, M. L.; Schlemper, E. O.; Murmann, R. K. "Structure of Dipotassium Ferrate(VI)" Acta Crystallographica 1982, volume B38, pp. 2237-2239. doi:10.1107/S0567740882008395.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Potassium_ferrate". A list of authors is available in Wikipedia.
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