Potassium sulphate (UK) or potassium sulfate (US) is an inorganic chemical compound which is also known as sulfate of potash, arcanite or was previously also known as potash of sulfur. It is an ionic compound which when dissolved in water dissociates into two ions - potassium cation and sulphate anion. By definition, a sulfate or sulphate ion is a polyatomic anion with an overall electrical charge of -2. On the other hand, Potassium can lose only one electron for attaining stable valence electronic configuration. Hence, from these facts, you can easily determine that the neutral potassium sulfate formula will have two cations of potassium and one anion of sulphate. Hence, the chemical formula of potassium sulphate is given as K2SO4. Thus, K2SO4 is the answer to be given when asked what is the chemical formula of potassium sulphate or what is the potassium sulphate chemical formula.
General Properties of Potassium Sulphate
Potassium sulphate is a white and odourless solid and is more commonly known for its useful properties as a fertilizer. It serves as a good source of potassium and sulfur for the plants as is depicted by the formula for potassium sulphate.
From the potassium sulphate formula or the potassium sulfate formula (whichever you are comfortable with), it is easy to calculate one of the physical properties of the compound - the molar mass. The molar mass of potassium sulphate as determined by the potassium sulphate formula is 174.26 /mol. Some of the other physical properties that cannot be obtained from potassium sulfate formula are noted below:
The density of the compound is 2.7 g/cm3.
The boiling point and the melting point of potassium sulphate are high. They are 1689℃ and 1069℃ respectively.
The ionic compound is highly soluble in water, sparingly soluble in glycerol solution and insoluble in solutions made up of acetone, alcohol, and cesium sulphide.
It is a non-flammable inorganic compound.
The crystals of potassium sulphate are transparent, very hard and are bitter and salty in taste.
Structural Characterisation of Potassium Sulphate
The structural formula of potassium sulphate shows the two potassium ions around the sulphate ions as depicted by the molecular formula of potassium sulphate. It is represented as follows:
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Potassium sulphate is naturally available in the mineral form of arcanite. It is a relatively rare mineral and hence more potassium sulphate can be found in the cocrystallization of potassium sulphate with magnesium sulphate, calcium sulphate or sodium sulphate. The crystal structure of the potassium sulphate mineral is orthorhombic. It exists in two crystalline forms - 𝛽-K2SO4 and 𝛼-K2SO4. Of the two, the 𝛽-K2SO4 is the common form and it converts into the 𝛼-K2SO4 form above the temperature of 583℃. Both of these forms are complex structures with sulphate ions adopting their typical tetrahedral structure. The structure of 𝛽-K2SO4 is as shown in the image below, with the yellow dots being sulphate anions surrounded by the two potassium cations:
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When the salt of potassium sulphate is heated in water with continuous swirling in a beaker, on settling, the crystals are observed to form a multi-arm spiral structure. These crystals are not known to form any hydrated compounds unlike sodium sulphate even though both the cations belong to the same group in the periodic table.
Industrial Production and Utilization of Potassium Sulphate
The most usual industrial method used for the production of potassium sulphate salt is by reacting potassium chloride with sulfuric acid. It produces potassium bisulphate as a product at the end of the first reaction. In the second step of the reaction, the newly formed potassium bisulphate reacts with potassium chloride to produce potassium sulphate. Both the reactions are given below, showing the balanced stoichiometry and chemical formula of potassium sulfate and other compounds:
KCl + H2SO4 → KHSO4 + HCl (First step: an exothermic reaction)
KHSO4 + KCl → K2SO4 + HCl (Second step: an endothermic reaction)
The main utilization of industrially produced potassium sulphate is for its use as a fertilizer. Along with being a source of both potassium and sulphur it also does not chloride which is harmful to the crops, thus making it a suitable fertilizer. The crude form of the salt is also sometimes used for the manufacturing of glass, as a flash reducer in artillery propellant charges, as an alternative blast media similar to soda blasting and also in pyrotechnics along with potassium nitrate for the generation of purple flame.