Potassium sulfate

Potassium sulfate
Arcanite
Other names Potassium sulphate
Identifiers
CAS number	7778-80-5 Y
PubChem	24507
ChemSpider	22915 Y
UNII	1K573LC5TV Y
KEGG	D01726 N
ChEBI	CHEBI:32036
ChEMBL	CHEMBL1201793
RTECS number	TT5900000
Jmol-3D images	Image 1
SMILES [K+].[K+].[O-]S([O-])(=O)=O
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
Properties
Molecular formula	K2SO4
Molar mass	174.259 g/mol
Appearance	White solid
Density	2.66 g/cm3[1]
Melting point	1069 °C, 1342 K, 1956 °F
Boiling point	1689 °C, 1962 K, 3072 °F
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
Structure
Crystal structure	orthorhombic
Hazards
MSDS	External MSDS
EU Index	Not listed
R-phrases	R22
S-phrases	S36
Main hazards	Irritant
Flash point	Non-flammable
LD50	6600 mg/kg
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
N sulfate (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 is commonly used in fertilizers, providing both potassium and sulfur.

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.^[2][3]

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 cocrystalisations of potassium sulfate and sulfates of magnesium calcium and sodium.

The minerals are:

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

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

Kieserite, MgSO₄·2H₂O, can be combined with a solution of potassium chloride to produce potassium sulfate.

Manufacture

The process for manufacturing potassium sulfate is similar to that used for the manufacture of sodium sulfate.

Potassium sulfate can be synthesised by reaction of potassium chloride with sulfuric acid according to the Leblanc process. Potassium sulfate is produced according to the following reaction:

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 off. SO₂ is produced through the burning of sulfur.

Properties

The anhydrous crystals form a double six-sided pyramid, but are in fact 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. It melts at 1067 °C.^[4]

Uses

The principal 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.^[5]

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.

Potassium hydrogen sulfate

Potassium hydrogen sulfate or bisulfate, KHSO₄, is readily produced by mixing K₂SO₄ with an equivalent number of moles of sulfuric acid. It forms rhombic pyramids, which melt at 197 °C. It dissolves in three parts of water at 0 °C. 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.

References

1. ^ Patnaik, Pradyot (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0070494398. 
2. ^ De Milt, Clara (1942). "Christopher Glaser". Journal of Chemical Education 19 (2): 53. doi:10.1021/ed019p53. 
3. ^ Klooster, van (1959). "Three centuries of Rochelle salt". Journal of Chemical Education 36 (7): 314. doi:10.1021/ed036p314. 
4. ^ Windholtz, M(Ed.)& Budavari, S (Ed). (1983). The Merck Index, Rahay: Merck & Co.
5. ^ Fertilizer manual (3rd ed. ed.). Dordrecht: Kluwer academic publ.. 1998. pp. 615. ISBN 0-7923-5032-4. 

• mindat.org: Arcanite
• webmineral: Arcanite

See also

• Arcanum duplicatum, the term for this substance in alchemy