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Potassium sulfate

Potassium sulfate
Other names Potassium sulphate
CAS number 7778-80-5
Molar mass 174.259 g/mol (anhydrous)
Appearance White crystalline solid
Density 2.66 g/cm3, anhydrous
Solubility in water 11.1 g/100 ml (20 °C)
Crystal structure orthorhombic
MSDS External MSDS
Main hazards Irritant
R/S statement None
Related Compounds
Other anions Potassium hydrogen sulfate
Potassium sulfite
Potassium bisulfite
Potassium persulfate
Other cations Lithium sulfate
Sodium sulfate
Magnesium sulfate
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Potassium sulfate (K2SO4) (in British English potassium sulphate 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.



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.

Natural resources

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• H20
  • Schönite K2SO4 • MgSO4 • 6 H20
  • Leonite K2SO4 • MgSO4 • 4 H20
  • Langbeinite K2SO4 • 2 MgSO4
  • Glaserite K3Na(SO4)2
  • Polyhalite K2SO4 • MgSO4 • 2 CaSO4 • 2 H20

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 H20 can be transformed and then the potassium sulfate can be dissolved in water.


  • 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.
  • It is obtained as a by-product in many chemical reactions including the production of nitric acid. This can be done by mixing the following: 2 Parts Potassium Nitrate to 1 Part Sulfuric Acid (molar ratio).

2KNO3 + H2SO4 ---> 2HNO3 + K2SO4

To purify the crude product, it can be dissolved in hot water and then filtered and cooled, causing the bulk of the dissolved salt to crystallize with characteristic promptitude.


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.


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


    This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Potassium_sulfate". A list of authors is available in Wikipedia.
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