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Aluminium sulfate is rarely, if ever, encountered as the anhydrous salt. It forms a number of different hydrates, of which the hexadecahydrate Al 2 (SO 4) 3 ·16H 2 O and octadecahydrate Al 2 (SO 4) 3 ·18H 2 O are the most common. The heptadecahydrate, whose formula can be written as [Al(H 2 O) 6] 2 (SO 4) 3 ·5H 2 O, occurs naturally as the ...
4 ·22 H 2 O, NaAl(SO 4) 2 ·6 H 2 O, MgSO 4 ·7H 2 O and Al 2 (SO 4) 3 ·17 H 2 O. [3] [4] The Ancient Greek Herodotus mentions Egyptian alum as a valuable commodity in The Histories. [5] The production of potassium alum from alunite is archaeologically attested on the island Lesbos. [6]
It crystallizes in an octahedral structure in neutral solution and cubic structure in an alkali solution with space group Pa 3 and lattice parameter of 12.18 Å. [4] The compound is the most important member of the generic class of compounds called alums, and is often called simply alum. [5]
Alkyl sulfates if ingested are well-absorbed and are metabolized into a C 3, C 4 or C 5 sulfate and an additional metabolite. The highest irritant of the alkyl sulfates is sodium laurylsulfate, with the threshold before irritation at a concentration of 20%. Surfactants in consumer products are typically mixed, reducing likelihood of irritation.
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
A stable derivative of aluminium monoiodide is the cyclic adduct formed with triethylamine, Al 4 I 4 (NEt 3) 4. Also of theoretical interest but only of fleeting existence are Al 2 O and Al 2 S. Al 2 O is made by heating the normal oxide, Al 2 O 3 , with silicon at 1,800 °C (3,272 °F) in a vacuum .
Ammonium iron(III) sulfate, NH 4 Fe(SO 4) 2 ·12 H 2 O, or NH 4 [Fe(H 2 O) 6](SO 4) 2 ·6 H 2 O, also known as ferric ammonium sulfate (FAS) or iron alum, is a double salt in the class of alums, which consists of compounds with the general formula AB(SO 4) 2 · 12 H 2 O. [2] It has the appearance of weakly violet, octahedrical crystals.
Other related compounds, sometimes called sodium aluminate, prepared by reaction of Na 2 O and Al 2 O 3 are Na 5 AlO 4 which contains discrete AlO 4 5− anions, Na 7 Al 3 O 8 and Na 17 Al 5 O 16 which contain complex polymeric anions, and NaAl 11 O 17, once mistakenly believed to be β-alumina, a phase of aluminium oxide.