Potassium sulfate

Potassium sulfate

Arcanite
Names
Other names Potassium sulphate
Identifiers
CAS Number	7778-80-5 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:32036 Y
ChemSpider	22915 Y
ECHA InfoCard	100.029.013
E number	E515 (acidity regulators, ...)
KEGG	D01726 Y
PubChem CID	24507
RTECS number	TT5900000
UNII	1K573LC5TV Y
InChI InChI=1S/2K.H2O4S/c;;1-5(2,3)4/h;;(H2,1,2,3,4)/q2*+1;/p-2 Y Key: OTYBMLCTZGSZBG-UHFFFAOYSA-L Y InChI=1/2K.H2O4S/c;;1-5(2,3)4/h;;(H2,1,2,3,4)/q2*+1;/p-2 Key: OTYBMLCTZGSZBG-NUQVWONBAU
SMILES [K+].[K+].[O-]S([O-])(=O)=O
Properties
Chemical formula	K2SO4
Molar mass	174.259 g/mol
Appearance	White solid
Odor	odorless
Density	2.66 g/cm3[1]
Melting point	1,069[2] °C (1,956 °F; 1,342 K)
Boiling point	1,689 °C (3,072 °F; 1,962 K)
Solubility in water	111 g/L (20 °C) 120 g/L (25 °C) 240 g/L (100 °C)
Solubility	slightly soluble in glycerol insoluble in acetone, alcohol, CS2
Magnetic susceptibility (χ)	−67.0·10−6 cm3/mol
Refractive index (nD)	1.495
Structure
Crystal structure	orthorhombic
Hazards
Main hazards	Irritant
Safety data sheet	External MSDS
R-phrases (outdated)	R22
S-phrases (outdated)	S36
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	6600 mg/kg (oral, rat)[3]
Related compounds
Other anions	Potassium selenate Potassium tellurate
Other cations	Lithium sulfate Sodium sulfate Rubidium sulfate Caesium sulfate
Related compounds	Potassium hydrogen sulfate Potassium sulfite Potassium bisulfite Potassium persulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Potassium sulfate (K₂SO₄) (in British English potassium sulphate, also called sulphate of potash, arcanite, or archaically known as potash of sulfur) is a non-flammable white crystalline salt which is soluble in water. The chemical compound is commonly used in fertilizers, providing both potassium and sulfur.

When potassium sulfate is heated in water and subjected to swirling in a beaker, the crystals form a multi-arm spiral structure when allowed to settle.^[4] Potassium sulfate could be used to study spiral structures in the laboratory.

History

Potassium sulfate (K₂SO₄) has been known since early in the 14th century, and it was studied by Glauber, Boyle, and Tachenius. In the 17th century, it was named arcanuni or sal duplicatum, as it was a combination of an acid salt with an alkaline salt. It was also known as vitriolic tartar and Glaser's salt or sal polychrestum Glaseri after the pharmaceutical chemist Christopher Glaser who prepared it and used medicinally.^[5][6]

Natural resources

The mineral form of potassium sulfate, arcanite, is relatively rare. Natural resources of potassium sulfate are minerals abundant in the Stassfurt salt. These are cocrystallizations of potassium sulfate and sulfates of magnesium calcium and sodium.

Relevant minerals are:

• Kainite, MgSO₄·KCl·H₂O
• Schönite, K₂SO₄·MgSO₄·6H₂O
• Leonite, K₂SO₄·MgSO₄·4H₂O
• Langbeinite, K₂Mg₂(SO₄)₃
• Glaserite, K₃Na(SO₄)₂
• Polyhalite, K₂SO₄·MgSO₄·2CaSO₄·2H₂O

The potassium sulfate can be separated from some of these minerals, like kainite, because the corresponding salt is less soluble in water.

Kieserite, MgSO₄·H₂O, can be combined with a solution of potassium chloride to produce potassium sulfate.

Production

Approximately 1.5 million tons were produced in 1985, typically by the reaction of potassium chloride with sulfuric acid, analogous to the Leblanc process. Potassium sulfate is produced according to the following reaction, which is conducted in so-called Mannheim furnaces:^[7]

2 KCl + H₂SO₄ → 2 HCl + K₂SO₄

The Hargreaves process uses sulfur dioxide, oxygen and water and potassium chloride as the starting materials to produce potassium sulfate. Hydrochloric acid evaporates. SO₂ is produced through the burning of sulfur.

Structure and properties

Two crystalline forms are known. Orthorhombic β-K₂SO₄ is the common form, but it converts to α-K₂SO₄ above 583 °C.^[7] These structures are complex, although the sulfate adopts the typical tetrahedral geometry.^[8]

• 
  Structure of β-K₂SO₄.
• 
  Coordination sphere of one of two types of K⁺ site.
• 
  SO4 environment in β-K₂SO₄.

It does not form a hydrate, unlike sodium sulfate. The salt crystallize as double six-sided pyramids, classified as rhombic. They are transparent, very hard and have a bitter, salty taste. The salt is soluble in water, but insoluble in solutions of potassium hydroxide (sp. gr. 1.35), or in absolute ethanol.

Uses

The dominant use of potassium sulfate is as a fertilizer. K₂SO₄ does not contain chloride, which can be harmful to some crops. Potassium sulfate is preferred for these crops, which include tobacco and some fruits and vegetables. Crops that are less sensitive may still require potassium sulfate for optimal growth if the soil accumulates chloride from irrigation water.^[9]

The crude salt is also used occasionally in the manufacture of glass. Potassium sulfate is also used as a flash reducer in artillery propellant charges. It reduces muzzle flash, flareback and blast overpressure.

It is sometimes used as an alternative blast media similar to soda in soda blasting as it is harder and similarly water-soluble.^[10]

Reactions

Acidification

Potassium hydrogen sulfate (also known as potassium bisulfate), KHSO₄, is readily produced by reacting K₂SO₄ with sulfuric acid. It forms rhombic pyramids, which melt at 197 °C (387 °F). It dissolves in three parts of water at 0 °C (32 °F). The solution behaves much as if its two congeners, K₂SO₄ and H₂SO₄, were present side by side of each other uncombined; an excess of ethanol the precipitates normal sulfate (with little bisulfate) with excess acid remaining.

The behavior of the fused dry salt is similar when heated to several hundred degrees; it acts on silicates, titanates, etc., the same way as sulfuric acid that is heated beyond its natural boiling point does. Hence it is frequently used in analytical chemistry as a disintegrating agent. For information about other salts that contain sulfate, see sulfate.

Reduction

At high temperatures, it is reduced to potassium sulfide by the action of carbon monoxide.

See also

• Arcanum duplicatum, the term for this substance in alchemy

References

External links

• mindat.org: Arcanite
• webmineral: Arcanite