Chrome alum

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title: "Chrome alum" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["sulfates", "potassium-compounds", "chromium(iii)-compounds", "coordination-complexes", "double-salts"] topic_path: "general/sulfates" source: "https://en.wikipedia.org/wiki/Chrome_alum" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

| Name = Potassium chromium sulfate | ImageFile = Chrome alum.jpg | ImageFile_Ref = | ImageSize = 244 | ImageName = Sample of chrome alum in sample jar | IUPACName = Chromium potassium sulfate | OtherNames = Chromium alum |Section1={{Chembox Identifiers | CASNo = 10141-00-1

| UNII_Ref = | UNII = 579U79PAIC

| PubChem = 61489 | ChemSpiderID = 19968602 | EINECS = 233-401-6 | RTECS = GB6845000 | MeSHName = chrome+alum | SMILES = [K]OS(=O)(=O)O[Cr]1OS(=O)(=O)O1 | StdInChI = 1S/Cr.K.2H2O4S/c;;21-5(2,3)4/h;;2(H2,1,2,3,4)/q+3;+1;;/p-4 | InChI = 1/Cr.K.2H2O4S/c;;21-5(2,3)4/h;;2(H2,1,2,3,4)/q+2;+1;;/p-4 | StdInChIKey = OIDPCXKPHYRNKH-UHFFFAOYSA-J | InChIKey = HIZQQXDAMAATMK-XBHQNQODAZ |Section2={{Chembox Properties | Formula = KCr(SO4)2 | Appearance = dark purple needles or greyish-brown powder when anhydrous | MolarMass = 283.220 g/mol | Density = 1.83 g cm−3 | MeltingPtC = 89 | BoilingPtC = 400 | Solubility = 24 g/100mL (at 20 °C) |Section3={{Chembox Hazards | GHSPictograms = | GHSSignalWord = WARNING | HPhrases = | PPhrases = |Section4={{Chembox Structure | CrystalStruct = cubic

Chrome alum or Chromium(III) potassium sulfate is the potassium double sulfate of chromium. Its chemical formula is KCr(SO4)2 and it is commonly found in its dodecahydrate form as KCr(SO4)2·12(H2O). It is used in leather tanning.

Production and properties

::figure[src="https://upload.wikimedia.org/wikipedia/commons/2/27/Chromium(III)_Potassium_Sulfate-crystals.jpg" caption="Chrome alum"] ::

Chromium alum is produced from chromate salts or from ferrochromium alloys. Concentrated aqueous solutions of potassium dichromate can be reduced, usually with sulfur dioxide but also with alcohols or formaldehyde, in the presence of sulfuric acid at temperatures 4)2·6H2O, dihydrate KCr(SO4)2·2H2O, and the monohydrate KCr(SO4)2·H2O are known.

Uses

Chromium alum is used in the tanning of leather as chromium(III) stabilizes the leather by cross linking the collagen fibers within the leather. However, this application is obsolete because the simpler chromium(III) sulfate is preferred.

It was also used in gelatine emulsions in photographic film as hardener.

References

References

  1. Holleman, Arnold F.. (1985). "Lehrbuch der Anorganischen Chemie". Walter de Gruyter.
  2. Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger, "Chromium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. {{doi. 10.1002/14356007.a07_067
  3. Brown, E. M.. (1997). "A Conformational Study of Collagen as Affected by Tanning Procedures". Journal of the American Leather Chemists Association.
  4. British Journal of Photography, vol 23 https://archive.org/details/britishjournalof35unse/page/478/mode/2up

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sulfatespotassium-compoundschromium(iii)-compoundscoordination-complexesdouble-salts