Iron(II)-potassium sulfate

Iron(II)-potassium sulfate
Names:	dipotassium-iron sulfate ferrous potassium sulfate potassium iron sulfate potassium Mohr's salt potassium iron schoenite KISH KFSH KFeSH
Formula:	K2Fe(SO4)2 (anhydrous) K2Fe(SO4)2 · 6H2O (hexahydrate)
Molar mass:	326.163 g/mol (anhydrous) 434.252 g/mol (hexahydrate)
Density:	2.169 g/cm3 (anhydrous)
Crystal system:	monoclinic (hexahydrate) a=9.0766 Å, b=12.2646 Å, c=6.1689 Åα=90°, β=104.548°, γ=90° monoclinic (tetrahydrate) a=11.837 Å, b=9.547 Å, c=9.939 Åα=90°, β=94.88°, γ=90° triclinic (dihydrate) a=7.308 Å, b=10.816 Å, c=6.531 Åα=109.03°, β=94.88°, γ=94.53°
Shapes:	https://en.crystalls.info/w/uploads/media/3/35/Deformed_tetragonal_bipyramid.json Deformed tetragonal bipyramid https://en.crystalls.info/w/uploads/media/7/7b/Beveled_rhombic_prism.json Beveled rhombic prism https://en.crystalls.info/w/uploads/media/9/9a/Truncated_deformed_hexagonal_prism.json Truncated deformed hexagonal prism https://en.crystalls.info/w/uploads/media/9/91/Truncated_trigonal_prism.json Truncated trigonal prism
Color:	light-green pale-green
Decomposition point:	200 °C473.15 K <br />392 °F <br />851.67 °R <br /> (hexahydrate)
Refractive index:	1.497 (tetrahydrate)
Stability:	stable (hexahydrate) hygroscopic (anhydrous)
Hardness:	relatively strong (2 on Moh's scale)
Toxicity:	non-toxic

Description

Inorganic compound, double salt of transitional metal iron, aklaline metal potassium and inorganic sulfuric acid. From water solutions crystallizes as hexahydrate.

Minerals

Occurs in nature as mereiterite mineral.

Precursors

Reaction between iron(II) and potassium sulfates

Chemical equation:

K₂SO₄ + FeSO₄ = K₂Fe(SO₄)₂↓

For preparation of 100.00g of iron(II)-potassium sulfate hexahydrate

hexahydrate

anhydrous

а 64.02g of iron(II) sulfate heptahydrate

heptahydrate

tetrahydrate

anhydrous

and 40.13g of potassium sulfate is required.

Dissolve compounds in hot water apart and then mix solutions into one container with intense stirring. Cooling or evaporation of a solution will cause double salt crystallyzation. Filter precipitate and wash it wish small amount of ethanol or acetone, then filter the solution and use it for crystal growing.

Reaction between iron(II) chloride or nitrate and potassium sulfate

Chemical equation:

2K₂SO₄ + FeCl₂ = K₂Fe(SO₄)₂↓ + 2KCl

2K₂SO₄ + Fe(NO₃)₂ = K₂Fe(SO₄)₂↓ + 2KNO₃

For preparation of 100.00g of iron(II)-potassium sulfate hexahydrate

hexahydrate

anhydrous

а 45.78g of potassium chloride tetrahydrate

tetrahydrate

anhydrous

or 66.31g of iron(II) nitrate hexahydrate

hexahydrate

nonahydrate

anhydrous

and 80.26g of sulfate is required.

Add to the flask with saturated iron compound solution a potassium sulfate solution with stirring. Freezing this mixture will cause forming a large amount of crystalline precipitateof Mohr's salt. For purifying compound from unreacted compounds add large amount of cold ethanol or acetone to solution, salt will settle to the bottom in the form of fine crystals or powder. Filter precipitate and wash it with small amount of the same solvent, then filter the solution and use it for crystal growing.

Reaction between iron(II) sulfate and potassium nitrate or chloride

Chemical equation:

2KCl + 2FeSO₄ = K₂Fe(SO₄)₂↓ + 2FeCl₂

2KNO₃ + 2FeSO₄ = K₂Fe(SO₄)₂↓ + 2Fe(NO₃)₂

For preparation of 100.00g of iron(II)-potassium sulfate hexahydrate

hexahydrate

anhydrous

а 34.34g of potassium chloride or 46.56g of nitrate and 128.04g of iron(II) sulfate heptahydrate

heptahydrate

tetrahydrate

anhydrous

is required.

Add to the flask with saturated iron(II) sulfate solution a potassium salt solution with stirring. Freezing this mixture will cause forming a large amount of crystalline precipitateof Mohr's salt. For purifying compound from unreacted compounds add large amount of cold ethanol or acetone to solution, salt will settle to the bottom in the form of fine crystals or powder. Filter precipitate and wash it with small amount of the same solvent, then filter the solution and use it for crystal growing.

Reaction between iron potassium alum, pure iron and sulfuric acid

Chemical equation:

2KFe(SO₄)₂ + Fe + 3H₂SO₄ = K₂Fe(SO₄)₂↓ + Fe₂(SO₄)₃ + 3H₂↑

For preparation of 100.00g of iron(II)-potassium sulfate hexahydrate

hexahydrate

anhydrous

а 132.21g of iron potassium alum, 12.86g of iron and 183.12g of 37%

37%

sulfuric acid is required.

Add diluted acid to the flask, then add small parts of iron with pure metal iron compound with stirring until it will totally dissolve . For purifying compound from unreacted compounds add large amount of cold ethanol or acetone to solution, salt will settle to the bottom in the form of fine crystals or powder. Filter precipitate and wash it with small amount of the same solvent, then filter the solution and use it for crystal growing.

Influence of impurities

Excess of iron(II) sulfate influenses on crystal shape and leads to growth of polycrystalline.
Excess of potassium sulfate influenses on crystal shape and leads to transparency deterioration.
Addition of glycerol leads to flattening of crystal shape and positively influences on transparency.

Storage conditions

Keep in its original form or under several layers of varnish at average humidity and room temperature. Do not keep crystals near heaters.

Solubility

TableGraph

Temperature	g/100,00 g water
0°C273.15 K <br />32 °F <br />491.67 °R <br />	27.9
70°C343.15 K <br />158 °F <br />617.67 °R <br />	82
100°C373.15 K <br />212 °F <br />671.67 °R <br />	109

Insoluble in ethanol and acetone.

Gallery

• 

  Iron(II)-potassium sulfateRostislav Dolgikh, VKontakteRostislav DolgikhVKontakte

• 

  Iron(II)-potassium sulfateRostislav Dolgikh, VKontakteRostislav DolgikhVKontakte

• 

  Iron(II)-potassium sulfateRostislav Dolgikh, VKontakteRostislav DolgikhVKontakte

Sources

• R.A.Kiper Properties of compounds. Handbook
• P.Ballirano, Rietveld refinement of the Tutton salt K2Fe(SO4)2 · 6H2O
• B.Hertweck, The crystal structures of the low-temperature phases of leonite-type compounds, K2Me(SO4)2 · 4H2O

Navigation

Potassium compounds
Salts	Potassium bromate (KBrO3) • Potassium bromide (KBr) • Potassium chlorate (KClO3) • Potassium chloride (KCl) • Potassium chromate (K2CrO4) • Potassium dihydrophosphate (KH2PO4) • Potassium dichromate (K2Cr2O7) • Potassium iodide (KI) • Potassium hydrofluoride (KHF2) • Potassium hydrophosphate (K2HPO4) • Potassium hydrophthalate (KC8H6O4) • Potassium metavanadate (KVO3) • Potassium nitrate (KNO3) • Potassium sulfate (K2SO4) • Potassium thiocyanate (KNCS)
Double salts	Aluminum-potassium sulfate (KAl(SO4)2) • Antimony(III)-potassium tartrate (K2Sb2(C4H2O6)2) • Chromium(III)-potassium sulfate (KCr(SO4)2) • Cobalt(II)-potassium sulfate (K2Co(SO4)2) • Copper(II)-potassium sulfate (K2Cu(SO4)2) • Indium(III)-potassium sulfate (KIn(SO4)2) • Iron(II)-potassium sulfate (K2Fe(SO4)2) • Iron(III)-potassium sulfate (KFe(SO4)2) • Lithium-potassium sulfate (KLiSO4) • Magnesium-potassium sulfate (K2Mg(SO4)2) • Magnesium-potassium sulfate-chromate (K2CrO4 · MgSO4) • Manganese(II)-potassium sulfate (K2Mn(SO4)2) • Nickel-potassium sulfate (K2Ni(SO4)2) • Potassium-sodium tartrate (KNaC4H4O6) • Vanadium(III)-ammonium sulfate (NH4V(SO4)2) • Zinc-potassium sulfate (K2Zn(SO4)2)
Complexes	Potassium dioxalatocuprate(II) (K2[Cu(C2O4)2]) • Potassium hexanitrocobaltate(III) (K3[Co(NO2)6]) • Potassium hexachlororhodiate(III) (K3[RhCl6]) • Potassium hexacyanocobaltate(III) (K3[Co(CN)6]) • Potassium hexacyanoferrate(II) (K4[Fe(CN)6]) • Tripotassium-sodium hexacyanoferrate(II) (K3Na[Fe(CN)6]) • Potassium hexacyanoferrate(III) (K3[Fe(CN)6]) • Potassium hexacyanochromate(III) (K3[Co(CN)6]) • Potassium tetraiodobismuthate (К[BiI4]) • Potassium tetraiodomercurate(II) (K2[HgI4]) • Potassium trioxalatoaluminate (K3[Al(C2O4)3]) • Potassium trioxalatocobaltate(III) (K3[Co(C2O4)3]) Potassium trioxalatoferrate(III) (K3[Fe(C2O4)3]) • Potassium-sodium trioxalatoferrate(III) (K5Na[Fe(C2O4)3]2) • Dipotassium-sodium trioxalatoferrate(III) (K2Na[Fe(C2O4)3]) • Potassium trioxalatochromate(III) (K3[Cr(C2O4)3])