Calcium sulfate Formula
Calcium sulfate, also known as gysum, is a versatile inorganic salt, widely used as desiccant, raw material in chemical industry or building materials. Moreover, it can also be used as medicine.
Formula and structure: Calcium sulfate chemical formula is CaSO4 and its molecular weight is 136.34 g mol-1. Calcium sulfate has three hydrated form: the anhydrous (CaSO4), the dihydrated (CaSO4) and the hemi-hydrated form. It is formed by the cation calcium Ca+2 and the anion sulfate SO4-2, which form an orthorhombic or monoclinic structure. Its chemical structure can be written as below, in the common representations used for organic molecules.
Occurrence: Calcium sulfate can be found in nature as being part of mineral ores of gypsum. The mineral gypsum contain calcium sulfate dehydrated and can be found in many countries, particularly in geological formations as cavern. The anhydrous form is present in other mineral, known as anhydrite.
Preparation: The main source of calcium sulfate dihydrated is the extraction from gypsum while the mineral anhydride is used to recovery the calcium sulfate anhydrous. The anhydrous form can also be prepared from the dehydratation of pure gypsum by heating above 650 ºC.
Physical properties: Calcium sulfate is an odorless, white amorphous or crystalline solid or powder.Its density is 2.96 g mL-1 in anhydrous salt and 2.32 g mL-1 in the dihydrated salt. Its melting point is 1460 ºC and in higher temperature it decomposes. It is poorly soluble in water (0.21 g/100 mL at 20 ºC).
Chemical properties: Calcium sulfate is very studied due it causes the permanent hardness in water together the magnesium sulfate. The permanent hardness is different to the temporary hardness causes by calcium and magnesium carbonate owing in the first case, the sulfates cannot be removed by boiling the water. Calcium sulfate is poorly soluble in water due the calcium cation (from the second group of periodic table) is voluminous and forms a molecule that is inefficiently solvate by water molecules.
Uses: Calcium sulfate is used as a building material such as stucco, mainly because this salt is insoluble in water and additionally can be moldable. It is also used as a raw material to produce other building material as cement. The calcium sulfate is food industry as coagulant.
Health effects / safety hazards: Calcium sulfate is an eye or a respiratory system irritating. It is not flammable and does not react with other chemical compounds.