potassium sulfate

Potassium sulfate
Other names	Potassium sulphate
Identifiers
CAS number	[7778-80-5]
PubChem	24507
RTECS number	TT5900000
Properties
Molecular formula	K2SO4
Molar mass	174.259 g/mol
Appearance	White crystalline 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	11.1 g/100 ml (20 °C) 12 g/100 mL (25 °C) 24 g/100 mL (100 °C)
Solubility	slightly soluble in glycerol insoluble in acetone, alcohol, CS2
Structure
Crystal structure	orthorhombic
Hazards
MSDS	External MSDS
EU Index	Not listed
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
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 know as vitriolic tartar.

Natural resources

The mineral form of potassium sulfate, namely 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·MgSO₄·6 H₂O
• Leonite, K₂SO₄·MgSO₄·4 H₂O
• Langbeinite, K₂SO₄·2 MgSO₄
• Glaserite, K₃Na(SO₄)₂
• Polyhalite, K₂SO₄·MgSO₄·2 CaSO₄·2 H₂O

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

With potassium chloride kieserite MgSO₄ • 2 H₂O can be transformed and then the potassium sulfate can be dissolved in water.

Manufacture

• Potassium sulfate can be synthesised by the decomposition of potassium chloride with sodium sulfate.

• The Hargreaves method is basically the same process with different starting materials. Sulfur dioxide, oxygen and water (the starting materials for sulfuric acid) are reacted with potassium chloride. Hydrochloric acid evaporates off.

• Potassium Sulfate is produced by mixing the following:

Potassium Chloride and Sulfuric Acid(with molar ratio). 2KCl + H₂SO₄ → 2HCl + K₂SO₄

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 1078 °C.

Uses

The principal use of potassium sulfate is as a fertilizer. The crude salt is also used occasionally in the manufacture of glass.

Potassium hydrogen sulfate

Potassium hydrogen sulfate or bisulfate, KHSO₄, is readily produced by mixing K₂SO₄ with an equivalent no. 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.

See also

• arcanum duplicatum, the term for this substance in alchemy

1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398