Potassium sulfate
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| Potassium sulfate | |
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| General | |
| Systematic name | Potassium sulfate |
| Other names | Potassium sulphate |
| Molecular formula | K2SO4 |
| Molar mass | 174.27 g/mol (anhydrous) |
| Appearance | White crystalline solid |
| CAS number | [7778-80-5] |
| Properties | |
| Density | 2.66 g/cm3, anhydrous |
| Solubility in water | 11.1 g/100 ml (20 °C) |
| In ethanol | insoluble |
| Melting point | 1069°C (1342 K) |
| Boiling point | 1689°C (1962 K) |
| Structure | |
| Coordination geometry |
? |
| Crystal structure | orthorhombic |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | Irritant |
| R/S statement | None |
| RTECS number | |
| NFPA 704 | |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| 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 |
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Potassium sulfate (K2SO4) (also 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.
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[edit] 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.
[edit] 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 kieserit MgSO4 • 2 H20 can be transformed and then the potassium sulfate can be dissolved in water.
[edit] Manufacture
- Corresponding to the first synthesis form Johann Glauber potassium sulfate can be synthesised by the decomposition of potassium chloride with sulfuric acid, hydrogen chloride evaporates and can be used to produce hydrochloric acid.
- 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.
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.
[edit] Properties
The very beautiful (anhydrous) crystals form a double six-sided pyramid, but are in fact classified as rhombic. They are transparent, very hard and absolutely resistant to corrosion 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.
[edit] Uses
The principal use of potassium sulfate is as a fertilizer. The crude salt is also used occasionally in the manufacture of glass.
[edit] 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 of 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.
Similar is the behavior of the fused dry salt 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.
[edit] See also
- arcanum duplicatum, the term for this substance in alchemy
