Chromium (III) sulfate

Structural formula
${\displaystyle \mathrm {\ {\Biggl [}} }$ ${\displaystyle \mathrm {\ \!\ {\Biggr ]}_{3}} }$
General
Surname	Chromium (III) sulfate
other names	Chromium sulfate
Molecular formula	Cr 2 (SO 4 ) 3 (anhydrous) Cr 2 (SO 4 ) 3 · n H 2 O (hydrates)
Brief description	red-brown solid (anhydrous) green or purple solid (hydrates)
External identifiers / databases
CAS number 10101-53-8 (anhydrous) 15244-38-9 (monohydrate) 10031-37-5 (pentahydrate) EC number 233-253-2 ECHA InfoCard 100.030.217 PubChem 24930 ChemSpider 21241287 Wikidata Q417538
properties
Molar mass	392.16 g mol −1 (anhydrous) 608.43 g mol −1 (dodecahydrate)
Physical state	firmly
density	3.01 g cm −3 (anhydrate at 20 ° C)
Melting point	90 ° C
solubility	bad in water
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 302-332-315-317-319 P: 301 + 330 + 331-302 + 352
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Chromium (III) sulfate (Cr ₂ (SO ₄ ) ₃ ) is a salt of sulfuric acid .

presentation

Chromium (III) sulfate can be represented by the reduction of dichromates :

Chromium (III) sulfate can be produced by reacting potassium dichromate , sulfuric acid and hydrogen sulfide . Potassium sulphate and water are produced as by-products :

${\displaystyle \mathrm {4\ K_{2}Cr_{2}O_{7}+13\ H_{2}SO_{4}+3\ H_{2}S} }$   ${\displaystyle \mathrm {\rightarrow 4\ Cr_{2}(SO_{4})_{3}+4\ K_{2}SO_{4}+16\ H_{2}O} }$

Alternatively, for example, ethanol can also be used instead of hydrogen sulfide, whereby - in addition to chromium (III) sulfate - potassium sulfate, acetic acid and water are formed:

${\displaystyle \mathrm {2\ K_{2}Cr_{2}O_{7}+8\ H_{2}SO_{4}+3\ C_{2}H_{5}OH} }$   ${\displaystyle \mathrm {\rightarrow 2\ Cr_{2}(SO_{4})_{3}+2\ K_{2}SO_{4}+3\ CH_{3}COOH+11\ H_{2}O} }$

However, chromium (III) sulfate containing water of crystallization is obtained via these reactions. The anhydrate can be produced by removing the water of crystallization at 280 ° C in a stream of CO ₂ .

properties

Chromium (III) sulfate containing water of crystallization

Chromium (III) sulfate solution

Anhydrous chromium (III) sulfate forms red-brown, hexagonal crystals; with water of crystallization as the pentahydrate (Cr ₂ (SO ₄ ) ₃ · 5 H ₂ O) it is dark green. The dodecahydrate and octadecahydrate, on the other hand, are lavender to violet.

Absolutely anhydrous chromium (III) sulfate is insoluble in water, whereas the forms containing water of crystallization are water-soluble with the formation of blue to violet-colored aqua complexes , which change to green-colored sulfato complexes when heated.

The pentahydrate has a triclinic crystal structure, isotypic to that of copper sulfate pentahydrate.

use

Chromium (III) sulphate is used as a textile stain or for tanning leather. It is also used as a raw material for other chromium compounds.

Individual evidence

1. ↑ ^{a b} SLAC: PHYSICAL CONSTANTS OF INORGANIC COMPOUNDS (PDF; 391 kB).
2. ↑ ^{a b c} Entry on chromium (III) sulfate. In: Römpp Online . Georg Thieme Verlag, accessed on June 20, 2014.
3. ↑ ^{a b c} entry to chromium (III) sulphate in the GESTIS database of IFA , retrieved on September 4, 2016(JavaScript required) .
4. ↑ jtbaker.com: Chromium Sulfate .
5. ↑ ^{a b} Datasheet Chromium (III) sulfate hydrate, Reagent Grade at AlfaAesar, accessed on December 7, 2019 ( PDF )(JavaScript required) .
6. ↑ ^{a b} Gmelin's Handbook of Inorganic Chemistry - No. 52 Chromium, The compounds (without complex bonds with neutral ligands) , 8th edition Berlin, 1962.
7. ↑ Jander-Blasius: Textbook of analytical and preparative inorganic chemistry , 5th edition, S. Hirzel, Stuttgart-Leipzig 1965, p. 225
8. ↑ Georg Brauer (ed.) U. a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume III, Ferdinand Enke, Stuttgart 1981, ISBN 3-432-87823-0 , p. 1509.