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User:Brutulf/Ferric Ammonium Sulfate

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Template:Chembox new Ferric Ammonium Sulfate Doceahydrate, NH4Fe(SO4)2 · 12 H2O ('FAS'), is a double salt in the class of aluns, which consists of compunds with the general formula AB(SO4)2 · 12 H2O[1]. It has the appearance of weakly violet, octahedrical crystals. There has been some discussion regarding the origin of the crystals' colour, with some ascribing it to impurities in the compound[2], and others claiming it to be a property of the crystal itself[3]. FAS is paramagnetic[4], acidic and toxic towards microorganisms[5].

Areas of use for FAS include waste water treatment[6], tanning[7], production of dyestuffs[8], and as an etching agent in the production of electronic components[9]. It has been used in a wide area of applications, including adiabatic refrigation equipment[10], biochemical analysis[11] and organic synthesis[12].

Preparation

FAS can be prepared by crystallization from a solution of ferric sulfate and ammonium sulfate. Iron(II) in ferrous sulfate is oxidised to Iron(III) in ferric sulfate by addition of sulfuric and nitric acid. Upon addition of ammonium sulfate to the solution and damping in of the solution, ferric ammonium sulfate crystals will preticipate.

Oxidation: 6 FeSO4 + 2 HNO3 + 3 H2SO4 = 3 Fe2(SO4)3 + 2 NO + 4 H2O

Synthesis: Fe2(SO4)3 + (NH4)2SO4 = 2 NH4Fe(SO4)2 .: Procedure[13]:

Add 75 mL diluted sulfuric acid to a 250 mL Erlenmeyer flask. Dissolve 25 g iron(II) ammonium sulfate (Mohr's Salt) in the flask while heating. Add water if neccesary. Dissolve the neccesary amount of iron(II)sulfate heptahydrate. Add 5 mL nitric acid to oxidise the iron. Caution: The solution will boil violently if the acid is added too quickly. Boil the solution until no more red fumes rise from the solution.

Test the solution for Iron(II) ion by transferring a drop to a test tube and adding potassium(III)ironcyanide. If the contents of the test tube turns blue, Iron(II) ion is present, and more nitric acid needs to be added to complete the oxidation.

After oxidation, dampen in the solution to about half volume. If the solution becomes sluggish, slowly add water until it regains the consistency of water. Let the solution cool and stand. Crystallization might take several hours to days to start, but may in some cases be started by scratching the inside of the glass with a glass rod or adding a seeding crystal.


Crystals of ferric ammonium sulfate

References

  1. ^ Considine , Douglas M: “Chemical and process technology encyclopedia”, McGraw-Hill , New York , 1974, p. 993
  2. ^ Christensen, Odin T: “On the Cause of the Amethyst Color of Ferric Alum and of Mixed Crystals of Ferric and Manganic Alum.” Chem. Lab. Roy. Vet. Agr. Hochschule, Kgl. Danske Vidsk. Selsk. Forh. (1906), p. 173-95
  3. ^ Jane Bonnell and Edgar Philip Perman: "CCXXIX.—The colour of iron alum", J. Chem. Soc., Trans., 1921, 119, 1994 - 1997, DOI: 10.1039/CT9211901994
  4. ^ Cooke, Meyer, Wolf: “The Specific Heats of Three Paramagnetic salts at Very Low Temperatures” Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Volume 237, Issue 1210, p. 395-403.
  5. ^ Fei Wang et al: “Microcalorimetric investigation of the toxic action of ammonium ferric(III)sulfate on the metabolic activity of pure microbes:” doi:10.1016/j.etap.2007.11.004 Accesible via http://www.sciencedirect.com
  6. ^ Wiley Encyclopedia of inorganic chemistry: Volume 4, p. 1704:
  7. ^ Wiley Encyclopedia of inorganic chemistry: Volume 4, p. 1704:
  8. ^ Wiley Encyclopedia of inorganic chemistry: Volume 4, p. 1704:
  9. ^ Chen , et al: United States Patent 5518131 - ”Etching molydbenum with ferric sulfate and ferric ammonium sulfate”
  10. ^ Grant W. Wilson, Peter T. Timbie: Construction techniques for adiabatic demagnetization refrigerators using ferric ammonium alum. Cryogenics, *Volume 39, Number 4, (1999) , p. 319-322
  11. ^ J.C. Whitehorn: A system of blood analysis. Supplement II. Simplified method for the determination of chlorides in blood or plasma. *Journal of Biological Chemistry (1921), 45 p. 449-60.
  12. ^ Yu, Shanxin et al: "Application of ammonium ferric sulfate dodecahydrate in organic synthesis", General Review 2005: 17(1), p. 27-30.
  13. ^ Hecht, Horstmar: “Prãparative Anorganische Chemie”, Springer-verlag, Berlin, 1951. p. 127
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