Chromium(III) sulfate
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(aq)6)sulfate.svg)
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| Names | |
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| IUPAC name
Chromium(III) sulfate
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| Other names
Basic chromium sulfate, chromic sulfate
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| Identifiers | |
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3D model (JSmol)
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| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.030.217 |
| EC Number |
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PubChem CID
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| UNII |
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| UN number | 2240 3077 |
CompTox Dashboard (EPA)
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| Properties | |
| Cr2(SO4)3 • 12H2O | |
| Molar mass | 392.16 g/mol 608.363 g/mol (dodecahydrate) 716.45 g/mol (octadecahydrate) |
| Appearance | reddish-brown crystals (anhydrous), purple crystals (hydrated) |
| Density | 3.10 g/cm3 (anhydrous) 1.86 g/cm3 (pentadecahydrate) 1.709 g/cm3 (octadecahydrate) |
| Melting point | 90 °C |
| Boiling point | >700 °C (decomposes to chromic acid) |
| insoluble (anhydrous) soluble (hydrated) | |
| Solubility | soluble in alcohol practically insoluble in acid |
| +11,800·10−6 cm3/mol | |
| Hazards | |
| GHS labelling: | |
   
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| Warning | |
| H314, H317, H332, H334, H335, H340, H350, H373, H412 | |
| P201, P202, P260, P261, P264, P271, P272, P273, P280, P281, P285, P301+P330+P331, P302+P352, P303+P361+P353, P304+P312, P304+P340, P304+P341, P305+P351+P338, P308+P313, P310, P312, P314, P321, P333+P313, P342+P311, P363, P403+P233, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| NIOSH (US health exposure limits): | |
PEL (Permissible)
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TWA 1 mg/m3[1] |
REL (Recommended)
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TWA 0.5 mg/m3[1] |
IDLH (Immediate danger)
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250 mg/m3[1] |
| Safety data sheet (SDS) | MSDS |
| Related compounds | |
Other cations
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Aluminium sulfate |
Related double salts
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Chrome alum |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Chromium(III) sulfate usually refers to the inorganic compounds with the formula Cr2(SO4)3.x(H2O), where x can range from 0 to 18. Additionally, ill-defined but commercially important "basic chromium sulfates" are known. These salts are usually either violet or green solids that are soluble in water. It is commonly used in tanning leather.
Chromium(III) sulfates
[edit]Three chromium(III) sulfates are well characterized:
- Anhydrous chromium(III) sulfate, Cr2(SO4)3, (CAS #10101-53-8) is a violet solid that dissolves in water upon addition of a reducing agent.
- Hydrated chromium(III) sulfate, Cr2(SO4)3·18H2O, (CAS #13520-66-6) is a violet solid that readily dissolves in water to give the metal aquo complex, [Cr(H2O)6]3+. The formula of this compound can be written more descriptively as [Cr(H2O)6]2(SO4)3·6H2O. Six of the eighteen water molecules in this formula unit are water of crystallization.
- Hydrated chromium(III) sulfate, Cr2(SO4)3·15(H2O), (CAS #10031-37-5) is a green solid that also readily dissolves in water. It is obtained by heating the 18-hydrate material above 70 °C. Further heating yields the anhydrous sulfate.
A variety of other chromium(III) sulfates are known, but also contain hydroxide or oxide ligands. Most important commercially is basic chromium sulfate, which is thought to be [Cr2(H2O)6(OH)4]SO4 (CAS#39380-78-4).[2] It results from the partial neutralization of the hexahydrates. Other chromium(III) hydroxides have been reported.[3]
Production
[edit]Chromium(III) sulfate are commonly obtained from the wastes of chromate oxidations of various organic compounds. Anthraquinone and quinone are produced on large scale by the x treatment of respectively anthracene and phenol with chromic acid. A chromium(III) oxide byproduct is generated, which is readily extracted into sulfuric acid. Evaporation of these acidic solutions affords salts if hydrate chromium(III) sulfate. Extraction of chromite ore with sulfuric acid in the presence of some chromate gives solutions of chromium(III) sulfate contaminated with other metal ions. Similarly, dissolution of chrome alloys gives chromium(III) sulfate together with ferrous sulfate.[4]
Basic chromium(III) sulfate
[edit]Basic chromium sulfate is produced from chromate salts by reduction with sulfur dioxide, although other methods exist.[4][5] The reduction could formally be written:
- Na2Cr2O7 + 3 SO2 + H2O → Cr2(SO4)3 + 2 NaOH
Since 33% of the anion charges are due to hydroxy ions the basicity is 33% (but in tanning jargon it is known as 33% reduced). Products with higher basicities, e.g. 42% or 50% may be obtained by the addition of sodium carbonate, these are often used in combination with sodium formate. The sodium sulfate is often left in the technical product since it is inert with respect to the tanning process.
Natural occurrence
[edit]Three complex minerals that are in part Cr(III) sulfates: bentorite, reddingtonite, and putnisite.[6][7][8][9]
References
[edit]- ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0141". National Institute for Occupational Safety and Health (NIOSH).
- ^ Covington, A. D.; Lampard, G. S.; Menderes, O.; Chadwick, A. V.; Rafeletos, G.; O'Brien, P. "Extended X-ray absorption fine structure studies of the role of chromium in leather tanning" Polyhedron 2001, volume 20, 461–466. doi:10.1016/S0277-5387(00)00611-2
- ^ Riou, A.; Bonnin, A. (1982). "Structure de l'Hydroxysulfate de Chrome monohydrate". Acta Crystallographica B. 24 (5): 1968–38. doi:10.1107/S0567740881005001.
- ^ a b Gerd Anger; Jost Halstenberg; Klaus Hochgeschwender; Christoph Scherhag; Ulrich Korallus; Herbert Knopf; Peter Schmidt; Manfred Ohlinger. "Chromium Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a07_067. ISBN 978-3527306732.
- ^ CW Harland; J Simpson. "Chromium sulfate tanning powder" (PDF). Farmers Fertiliser Ltd - a subsidiary of Fernz Corporation Ltd. Archived from the original (PDF) on 2018-01-27. Retrieved 2016-08-04.
- ^ "Bentorite".
- ^ "Redingtonite".
- ^ "Putnisite".
- ^ "List of Minerals". 21 March 2011.