Chromium(III)-potassium sulfate

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Crystal compoundsSaltsSulfatesChromium(III)-potassium sulfate


  Chromium(III)-potassium sulfate   
Names: potassium-chromium(III) sulfate
monopotassium-chromium(III) sulfate
chromium-potassium alum

Formula: KCr(SO4)2 (anhydrous)
KCr(SO4)2 · 12H2O (dodecahydrate)
SMILES: [O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[Cr+3].[K+]
Molar mass: 283.216 g/mol (anhydrous)
499.395 g/mol (dodecahydrate)
Density: 1.842 g/cm3 (dodecahydrate)
Crystal system: hexagonal (anhydrous)
a=4.7261 Å
4.7261 Å
0.4726 nm
, b=4.7261 Å
4.7261 Å
0.4726 nm
, c=8.0483 Å
8.0483 Å
0.8048 nm
α=90°
90°  
, β=90°
90°  
, γ=120°
120°  

cubic (dodecahydrate)
a=12.2305 Å
12.2305 Å
1.2231 nm
, b=12.2305 Å
12.2305 Å
1.2231 nm
, c=12.2305 Å
12.2305 Å
1.2231 nm
α=90°
90°  
, β=90°
90°  
, γ=90°
90°  

Shapes:
https://media.crystalls.info/w/uploads/media/Octahedron.json
https://media.crystalls.info/w/uploads/media/Tetragonal_pyramid.json
https://media.crystalls.info/w/uploads/media/Truncated_octahedron.json
https://media.crystalls.info/w/uploads/media/Cuboctahedron.json

Color: violet
blue-violet
purple
red
Decomposition point: 89 °C
362.15 K
192.2 °F
651.87 °R
(dodecahydrate)
350 °C
623.15 K
662 °F
1,121.67 °R
(anhydrous)
Refractive index: 1.4564 (dodecahydrate)
Stability: erodes (dodecahydrate)
hygroscopic (anhydrous)
Hardness: strong
Toxicity: highly toxic

Description

Inorganic compound, double salt of transitional metal chromium, alkaline metal potassium and inorganic sulfuric acid. From water solutions crystallizes as dodecahydrate.

Precursors

Reaction between chromium and potassium sulfates

Chemical equation:

K2SO4 + Cr2(SO4)3 = 2KCr(SO4)2

For preparation of 100.00g of chromium(III)-potassium sulfate dodecahydrate а 60.91g of chromium(III) sulfate dodecahydrate and 17.45g 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.

Reaction between potassium dichromate, sulfuric acid and hydrogen peroxide

Chemical equation:

K2Cr2O7 + 3H2O2 + 4H2SO4 = 2KCr(SO4)2 + H2O

For preparation of 100.00g of chromium(III)-potassium sulfate dodecahydrate а 29.45g of potassium dichromate, 34.06g of 30% peroxide and 106.16g of 37% sulfuric acid is required.
Add to the flask with sulfuric acid solution hydrogen peroxide and then add small parts of potassium dichromate with stirring until a precipitation forming will stop. Filter precipitate and wash it wish small amount of ethanol or acetone, then filter the solution and use it for crystal growing.

Reaction between potassium dichromate, sulfuric acid and any reducing agentsuch as ethanol, isopropanol, oxalic acid, formic acid or glucose

Chemical equation:

K2Cr2O7 + 3C2H5OH + 4H2SO4 = 2KCr(SO4)2 + 3CH3COH + 7H2O
K2Cr2O7 + 3CH3CH(OH)CH3 + 4H2SO4 = 2KCr(SO4)2 + 3CH3C(O)CH3 + 7H2O
K2Cr2O7 + 3HOOCCOOH + 4H2SO4 = 2KCr(SO4)2 + 6CO2 + 7H2O
4K2Cr2O7 + 3CH3COOH + 16H2SO4 = 8KCr(SO4)2 + 6CO2 + 22H2O
4K2Cr2O7 + C6H12O6 + 16H2SO4 = 8KCr(SO4)2 + 22H2O + 6CO2

For preparation of 100.00g of chromium(III)-potassium sulfate dodecahydrate а 29.45g of potassium dichromate, 13.84g of ethanol or 18.05g of isopropanol or 27.04g of oxalic acid or 5.31g of 85% formic acid or 4.51g of glucose and 106.16g of 37% sulfuric acid is required.
Add to the flask saturated solution of sulfuric acid and potassium dichromate and then add small parts of hot reducing agent solution with heating and stirring. Emission of large amount of gas will begin.Attention, exuding gas irritates eyes and lungs! The synthesis should be carried out only in a fume hood or outdoors!

Reaction between pure chromium, potassium nitrate and sulfuric acid

Chemical equation:

2H2SO4 + KNO3 + Cr = KCr(SO4)2 + NO↑ + 2H2O

For preparation of 100.00g of chromium(III)-potassium sulfate dodecahydrate а 10.41g of chromium, 20.24g of potassium nitrate and 106.16g of 37% sulfuric acid is required.
Add acid to the flask, then add small parts of chromium compound with stirring until it will totally dissolve . After reaction will stop, filter the solution and use it for crystal growing.

Reaction between chromium(III) nitrate or chloride and potassium sulfate

Chemical equation:

2K2SO4 + Cr(NO3)3 = KCr(SO4)2 + 3KNO3
2K2SO4 + CrCl3 = KCr(SO4)2 + 3KCl

For preparation of 100.00g of chromium(III)-potassium sulfate dodecahydrate а 80.13g of chromium(III) nitrate nonahydrate or 53.35g of chromium(III) chloride hexahydrate and 69.79g 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, then filter the solution and use it for crystal growing.

Reaction between chromium(III) sulfate and nitrate or potassium chloride

Chemical equation:

3KNO3 + 2Cr2(SO4)3 = 3KCr(SO4)2 + Cr(NO3)3
3KCl + 2Cr2(SO4)3 = 3KCr(SO4)2 + CrCl3

For preparation of 100.00g of chromium(III)-potassium sulfate dodecahydrate а 81.21g of chromium(III) sulfate dodecahydrate and 20.24g of potassium nitrate or 14.93g of potassium chloride 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, then filter the solution and use it for crystal growing.

Reaction between potassium hydroxide or carbonate, chromium(III) hydroxide and sulfuric acid

Chemical equation:

2H2SO4 + KOH + Cr(OH)3 = KCr(SO4)2 + 4H2O
4H2SO4 + K2CO3 + 2Cr(OH)3 = 2KCr(SO4)2 + 7H2O + CO2

For preparation of 100.00g of chromium(III)-potassium sulfate dodecahydrate а 11.23g of potassium hydroxide or 13.84g of potassium carbonate, 20.63g of chromium(III) hydroxide and 106.16g of 37% sulfuric acid is required.
Add acid to the flask, then add small parts of potassium and chromium compound with stirring until it will totally dissolve or, if you use carbonate, until carbon dioxide emission will stop. After reaction will stop, filter the solution and use it for crystal growing.

Influence of impurities

Addition of borax has no affect on crystal shape, as it does with potassium alum.

Notes

Due to crystal erosion in the air, they are usually coated with a layer of potassium alum. Alums are isomorphous between each other, so they are not dissolving in saturated solution of other alums.
Also, you can combine alums in one solution, getting crystals of other shades.

Storage conditions

For crystal storing use hermetic vessel with small amount of saturated solution at the bottom or place wadding moistened with such solution. You can use such alternatives as vessel with vaseline or vegetable oil, organic non-hygroscopic solvent (kerosene, benzine or paraffin). Also you can use acrylate polymer or another kinds of solidifying plastic.

Solubility

Temperatureгр/100,00 гр water
0°C
273.15 K
32 °F
491.67 °R
3.9
3.9 g/100g
3.754 %
25°C
298.15 K
77 °F
536.67 °R
24.39
24.39 g/100g
19.608 %
Insoluble in ethanol and acetone.

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