calcium sulfate Chemical Properties
- Solubility Product Constant (Ksp)pKsp: 4.31
calcium sulfate Usage And Synthesis
- DescriptionCalcium sulfate,CaS04, is a grayish-white dense powder that occurs in nature in both an anhydrous form (anhydrite) and hydrated form(gypsum); it is also the byproduct of many chemical reactions. It has many industrial uses;for example, as a source of sulfur and sulfuric acid,in cements, tiles and plaster,as a soil conditioner, in paints, dyes,and polishes, and as a food additive.
- UsesPharmaceutic aid (tablet and capsule diluent).
- UsesCalcium Sulfate is a general additive available as both calcium sul- fate anhydrous, made by the high-temperature calcining of gypsum which is then ground and separated, and calcium sulfate dihydrate, which is made by grinding and separating gypsum containing about 20% water of crystallization. calcium sulfate anhydrous contains approximately 29% calcium, and calcium sulfate dihydrate contains approximately 23% calcium. it is used, among other things, as a filler and baking powder for standardization purposes; a firming agent in canned potatoes, tomatoes, carrots, lima beans, and pep- pers; in dough as a source of calcium ions (because the absence of calcium ions causes bread dough to be soft and sticky and to pro- duce bread of poor quality); in soft-serve ice cream to produce dry- ness and stiffness; as a calcium ion source for reaction with alginates to form dessert gels; and as a calcium source for food enrichment.
- UsesCalcium Sulfate is most often used as “gypsum” which is the dihydrate. In the form of b-anhydrite (the nearly anhydrous form), it is used as a desiccant. It is also used as a coagulant in products like “tofu”, which is a “bean curd”. When sold as a colorindicating variant under the name “Drierite ”, it appears blue or pink due to impregnation with cobalt chloride, which functions as a moisture indicator. In its natural state, unrefined calcium sulfate is a translucent, crystalline white rock. Many forms are known, including “Alabaster” and “Gypsum”. Selenite, Satin spar, Desert rose, and Gypsum flower are four varieties of Gypsum minerals; all four varieties are crystalline. The four “crystalline” varieties of gypsum are sometimes grouped together and called selenite. All have the same chemical formulation, CaSO4·2H2O. All varieties of gypsum are very soft minerals (hardness: 2 on Mohs scale). This is the most important identifying characteristic of gypsum.
- PreparationCalcium Sulfate may be
prepared by the addition of a soluble calcium salt to
a solution of sodium sulfate:
CaCl2＋ Na2SO4→CaSO4＋ 2NaCl
The product is generally a dihydrate although other hydrates are also known. The CAS numbers of these materials are: 7778-18-9 (anhydrite); 10034-76-1 (hemihydrate); 10101-41-4 (dihydrate).
- Industrial usesCalcium sulfate (CaSO4?2H2O) is the common blackboard chalk.
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