Potassium sulfate

Structural formula
__ K + __ S 6+ __ O 2−
Crystal system	orthorhombic
Space group	Pmcn (No. 62, position 5)
Lattice parameters	a = 5.7704  Å , b = 10.0712 Å, c = 7.4776 Å
General
Surname	Potassium sulfate
other names	Potassium sulfuric acid Tartarus vitriolatus Potassium sulfuricum SOP E 515 POTASSIUM SULPHATES ( INCI )
Molecular formula	K 2 SO 4
Brief description	colorless crystals or powder
External identifiers / databases
CAS number 7778-80-5 EC number 231-915-5 ECHA InfoCard 100.029.013 PubChem 24507 ChemSpider 22915 Wikidata Q193054
properties
Molar mass	174.26 g mol −1
Physical state	firmly
density	2.66 g cm −3
Melting point	1069 ° C
boiling point	1689 ° C
solubility	111 g l −1 at 20 ° C and 250 g l −1 at 100 ° C
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
Toxicological data	6600 mg kg −1 ( LD 50 ,  rat ,  oral ) 1530 mg l −1 ( LC 50 ,  fish , 96 h , median value) > 720 mg l −1 ( LC 50 ,  crustaceans , 48 h )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Potassium sulfate is the potassium salt of sulfuric acid . It is mainly used as a fertilizer .

history

The pharmacist and chemist Johann Rudolph Glauber was the first to produce the salt from potassium chloride and sulfuric acid, which has been known since the 14th century .

Occurrence

Arcanite

Picromerite

Pure potassium sulphate (K ₂ SO ₄ ) occurs naturally as the mineral arcanite .

In addition to ternary potassium sulfate, quaternary compounds with potassium and sulfate and another cation - so-called double salts - are known as minerals, such as belomarinaite (KNa [SO ₄ ]), leonite (K ₂ Mg [SO ₄ ] ₂ · 4H ₂ O) , Picromerite (K ₂ Mg [SO ₄ ] ₂ · 6H ₂ O), langbeinite (K ₂ Mg ₂ [SO ₄ ] ₃ ) and the potash whim (generally KM ^III (SO ₄ ) ₂ · 12H ₂ O).

Presentation and extraction

Initially, potassium sulfate was obtained from the mineral kainite (MgSO ₄ · KCl · 3 H ₂ O). However, this production method was soon abandoned in favor of more cost-effective processes based on potassium chloride.

One way in the production of potassium sulfate is the reaction of potassium chloride with sulfuric acid at a temperature of 700 ° C .

${\displaystyle {\ce {H2SO4{}+2KCl->[{\text{700 °C}}]K2SO4{}+2HCl}}}$

Alternatively, potassium sulfate is by double reaction with other metal sulfates such as. B. Magnesium sulfate can be represented:

${\displaystyle {\ce {2KCl + 2MgSO4 -> K2SO4.MgSO4 + MgCl2}}}$

${\displaystyle {\ce {K2SO4.MgSO4 + 2KCl -> 2K2SO4 + MgCl2}}}$

The so-called Hargreaves process uses the reaction of potassium chloride with a mixture of sulfur dioxide , air and water to produce potassium sulfate :

${\displaystyle {\ce {2KCl + SO2 + {\frac {1}{2}}O2 + H2O -> K2SO4 + 2HCl}}}$

Potassium sulfate is also a by-product in the production of nitric acid .

Potassium sulphate is easier to produce by reacting potassium hydroxide and sulfuric acid.

properties

The anhydrous crystals have orthorhombic symmetry ( space group Pmcn (space group no. 62, position 5) , lattice parameters a = 5.7704 Å, b = 10.0712 Å, c = 7.4776 Å). They are colorless and transparent, very hard and extremely stable in the air. Potassium sulfate has a bitter to salty taste. While it dissolves well in water, it is insoluble in ethanol .

use

Potassium sulfate is used for the production of potassium alum , potassium silicate , potassium persulfate , potassium , desensitizing agents , synthetic rubber and mixed fertilizers. In addition, it finds application in the Weinstein - and tartaric acid purification and diverse use in the dye -, explosives - and pharmaceutical industries.

Potassium sulfate is used in food technology as a firming agent , acid regulator or carrier . Potassium sulfate is used as a salt substitute in diet foods. It is approved in the EU as a food additive with the number E515 without a maximum quantity restriction ( quantum satis ) for all foods approved for additives.

It is also a component of potash fertilizers that are used to fertilize chloride- sensitive crops, for example in viticulture .

Potassium sulphate is also used as an active ingredient in extinguishing powders (mostly together with other alkali salts such as sodium hydrogen carbonate ) of fire classes B and C.

It is also used as a homeopathic medicine . As Schüßler salt , it is used there for all peeling skin diseases, such as neurodermatitis and psoriasis.

literature

• AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 1179.

Individual evidence

1. ↑ ^{a b} K. Ojima, Y. Nishihata, A. Sawada: Structure of potassium sulfate at Temperatures from 296 K down to 15 K . In: Acta Crystallographica Section B . tape 51 , 1995, p. 287-293 , doi : 10.1107 / S0108768194013327 .
2. ↑ Entry on POTASSIUM SULFATE in the CosIng database of the EU Commission, accessed on February 26, 2020.
3. ↑ ^{a b c d e f g h i} Entry on potassium sulfate in the GESTIS substance database of the IFA , accessed on December 21, 2019 (JavaScript required)
4. ↑ Entry on potassium sulfate. In: Römpp Online . Georg Thieme Verlag, accessed on March 24, 2019.