Iron(II)-potassium sulfate

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Crystal compoundsSaltsSulfatesIron(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)
SMILES: [O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[Fe+2].[K+].[K+]
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
9.0766 Å
0.9077 nm
, b=12.2646 Å
12.2646 Å
1.2265 nm
, c=6.1689 Å
6.1689 Å
0.6169 nm
α=90°
90°  
, β=104.548°
104°32′52.8″  
, γ=90°
90°  

monoclinic (tetrahydrate)
a=11.837 Å
11.8370 Å
1.1837 nm
, b=9.547 Å
9.5470 Å
0.9547 nm
, c=9.939 Å
9.9390 Å
0.9939 nm
α=90°
90°  
, β=94.88°
94°52′48.0″  
, γ=90°
90°  

triclinic (dihydrate)
a=7.308 Å
7.3080 Å
0.7308 nm
, b=10.816 Å
10.8160 Å
1.0816 nm
, c=6.531 Å
6.5310 Å
0.6531 nm
α=109.03°
109°1′48.0″  
, β=94.88°
94°52′48.0″  
, γ=94.53°
94°31′48.0″  

Color: light-green
pale-green
Decomposition point: 200 °C
473.15 K
392 °F
851.67 °R
(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 а 64.02g of iron(II) sulfate heptahydrate 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 а 45.78g of potassium chloride tetrahydrate or 66.31g of iron(II) nitrate hexahydrate 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 precipitationof 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 а 34.34g of potassium chloride or 46.56g of nitrate and 128.04g of iron(II) sulfate heptahydrate 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 precipitationof 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 а 132.21g of iron potassium alum, 12.86g of iron and 183.12g of 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

Store in its original form or under several layers of varnish at average humidity and room temperature. Do not store in matchboxes or cotton wool and do not heat.

Solubility

Temperatureгр/100,00 гр water
0°C
273.15 K
32 °F
491.67 °R
27.9
27.9 g/100g
21.814 %
10°C
283.15 K
50 °F
509.67 °R
~35.6
35.6 g/100g
26.254 %
15°C
288.15 K
59 °F
518.67 °R
~39.5
39.5 g/100g
28.315 %
20°C
293.15 K
68 °F
527.67 °R
~43.4
43.4 g/100g
30.265 %
25°C
298.15 K
77 °F
536.67 °R
~47.3
47.3 g/100g
32.111 %
30°C
303.15 K
86 °F
545.67 °R
~51.2
51.2 g/100g
33.862 %
40°C
313.15 K
104 °F
563.67 °R
~58.9
58.9 g/100g
37.067 %
50°C
323.15 K
122 °F
581.67 °R
~66.6
66.6 g/100g
39.976 %
60°C
333.15 K
140 °F
599.67 °R
~74.3
74.3 g/100g
42.628 %
70°C
343.15 K
158 °F
617.67 °R
82
82 g/100g
45.055 %
80°C
353.15 K
176 °F
635.67 °R
~91.0
91 g/100g
47.644 %
90°C
363.15 K
194 °F
653.67 °R
~100
100 g/100g
50 %
100°C
373.15 K
212 °F
671.67 °R
109
109 g/100g
52.153 %
Insoluble in ethanol and acetone.

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