Chromium(III)-ammonium sulfate

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Crystal compoundsSaltsSulfatesChromium(III)-ammonium sulfate


  Chromium(III)-ammonium sulfate   
Names: ammonium-chromium(III) sulfate
monoammonium-chromium(III) sulfate

Formula: NH4Cr(SO4)2 (anhydrous)
NH4Cr(SO4)2 · 12H2O (dodecahydrate)
SMILES: [O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[Cr+3].[NH4+]
Molar mass: 262.157 g/mol (anhydrous)
478.335 g/mol (dodecahydrate)
Density: 1.72 g/cm3 (dodecahydrate)
Crystal system: hexagonal (anhydrous)
α=90°
90°  
, β=90°
90°  
, γ=120°
120°  

cubic (dodecahydrate)
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
Melting point: 94 °C
367.15 K
201.2 °F
660.87 °R
(dodecahydrate)
Decomposition point: 700 °C
973.15 K
1,292 °F
1,751.67 °R
(anhydrous)
Stability: erodes (dodecahydrate)
hygroscopic (anhydrous)
Hardness: strong
Toxicity: slightly toxic
LD50=720mg/kg

Description

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

Precursors

Reaction between chromium and ammonium sulfates

Chemical equation:

(NH4)2SO4 + Cr2(SO4)3 = 2NH4Cr(SO4)2

For preparation of 100.00g of chromium(III)-ammonium sulfate dodecahydrate а 63.59g of chromium(III) sulfate dodecahydrate and 13.81g of ammonium 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 ammonium dichromate, sulfuric acid and hydrogen peroxide

Chemical equation:

(NH4)2Cr2O7 + 3H2O2 + 4H2SO4 = 2NH4Cr(SO4)2 + H2O

For preparation of 100.00g of chromium(III)-ammonium sulfate dodecahydrate а 26.35g of ammonium dichromate, 35.55g of 30% peroxide and 110.83g of 37% sulfuric acid is required.
Add to the flask with sulfuric acid solution hydrogen peroxide and then add small parts of ammonium 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 ammonium dichromate, sulfuric acid and any reducing agentsuch as ethanol, isopropanol, oxalic acid, formic acid or glucose

Chemical equation:

(NH4)2Cr2O7 + 3C2H5OH + 4H2SO4 = 2NH4Cr(SO4)2 + 3CH3COH + 7H2O
(NH4)2Cr2O7 + 3CH3CH(OH)CH3 + 4H2SO4 = 2NH4Cr(SO4)2 + 3CH3C(O)CH3 + 7H2O
(NH4)2Cr2O7 + 3HOOCCOOH + 4H2SO4 = 2NH4Cr(SO4)2 + 6CO2 + 7H2O
4(NH4)2Cr2O7 + 3CH3COOH + 16H2SO4 = 8NH4Cr(SO4)2 + 6CO2 + 22H2O
4(NH4)2Cr2O7 + C6H12O6 + 16H2SO4 = 8NH4Cr(SO4)2 + 22H2O + 6CO2

For preparation of 100.00g of chromium(III)-ammonium sulfate dodecahydrate а 26.35g of ammonium dichromate, 14.45g of ethanol or 18.85g of isopropanol or 28.23g of oxalic acid or 5.54g of 85% formic acid or 4.71g of glucose and 110.83g of 37% sulfuric acid is required.
Add to the flask saturated solution of sulfuric acid and ammonium 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, ammonium nitrate and sulfuric acid

Chemical equation:

2H2SO4 + NH4NO3 + Cr = NH4Cr(SO4)2 + NO↑ + 2H2O

For preparation of 100.00g of chromium(III)-ammonium sulfate dodecahydrate а 10.87g of chromium, 16.73g of ammonium nitrate and 110.83g 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 ammonium sulfate

Chemical equation:

2(NH4)2SO4 + Cr(NO3)3 = NH4Cr(SO4)2 + 3NH4NO3
2(NH4)2SO4 + CrCl3 = NH4Cr(SO4)2 + 3NH4Cl

For preparation of 100.00g of chromium(III)-ammonium sulfate dodecahydrate а 83.65g of chromium(III) nitrate nonahydrate or 55.70g of chromium(III) chloride hexahydrate and 55.25g of ammonium 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 ammonium chloride

Chemical equation:

3NH4NO3 + 2Cr2(SO4)3 = 3NH4Cr(SO4)2 + Cr(NO3)3
3NH4Cl + 2Cr2(SO4)3 = 3NH4Cr(SO4)2 + CrCl3

For preparation of 100.00g of chromium(III)-ammonium sulfate dodecahydrate а 84.79g of chromium(III) sulfate dodecahydrate and 16.73g of ammonium nitrate or 11.18g of ammonium 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 ammonia, chromium(III) hydroxide and sulfuric acid

Chemical equation:

2H2SO4 + NH4OH + Cr(OH)3 = NH4Cr(SO4)2 + 4H2O
4H2SO4 + (NH4)2CO3 + 2Cr(OH)3 = 2NH4Cr(SO4)2 + 7H2O + CO2

For preparation of 100.00g of chromium(III)-ammonium sulfate dodecahydrate а 29.31g of 25% ammonia, 21.54g of chromium(III) hydroxide and 110.83g of 37% sulfuric acid is required.
Add acid to the flask, then add small parts of ammonium 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 ammonium alum.

Notes

Due to crystal erosion in the air, they are usually coated with a layer of ammonium 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 %
10°C
283.15 K
50 °F
509.67 °R
~6.65
6.65 g/100g
6.235 %
15°C
288.15 K
59 °F
518.67 °R
~8.03
8.03 g/100g
7.433 %
20°C
293.15 K
68 °F
527.67 °R
~9.41
9.41 g/100g
8.601 %
25°C
298.15 K
77 °F
536.67 °R
10.78
10.78 g/100g
9.731 %
30°C
303.15 K
86 °F
545.67 °R
~12.4
12.4 g/100g
11.032 %
40°C
313.15 K
104 °F
563.67 °R
15.7
15.7 g/100g
13.57 %
Insoluble in ethanol and acetone.

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