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Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO 4 and related hydrates. In the form of γ- anhydrite (the anhydrous form), it is used as a desiccant . One particular hydrate is better known as plaster of Paris , and another occurs naturally as the mineral gypsum .
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
The tables below provides information on the variation of solubility of different substances (mostly inorganic compounds) in water with temperature, at one atmosphere pressure. Units of solubility are given in grams of substance per 100 millilitres of water (g/(100 mL)), unless shown otherwise.
A few, such as calcium sulfate and cerium(III) sulfate, become less soluble in water as temperature increases (ΔH < 0). [15] This is also the case for calcium hydroxide (portlandite), whose solubility at 70 °C is about half of its value at 25 °C. The dissolution of calcium hydroxide in water is also an exothermic process (ΔH < 0).
Calcium oxalate: 8.59 Calcium sulfate: 4.61 Calcium tartrate: 6.11 (18 °C) Copper(I) bromide: ... Solubility products of metal sulfides (data page) References
Solubility products are often expressed in logarithmic form. Thus, for calcium sulfate, with K sp = 4.93 × 10 −5 mol 2 dm −6, log K sp = −4.32. The smaller the value of K sp, or the more negative the log value, the lower the solubility. Some salts are not fully dissociated in solution.
English: The temperature dependence of the solubility of calcium sulfate in pure water. 3 phases are marked: gypsum (calcium sulfate dihydrate), hemihydrate (plaster of Paris), and anhydrite. Data source: "The ASME Handbook on Water Technology for Thermal Power Systems", Paul Cohen (ed), American Society of Mechanical Engineers, 1989.
Calcium sulfite, or calcium sulphite, is a chemical compound, the calcium salt of sulfite with the formula CaSO 3 ·x(H 2 O). Two crystalline forms are known, the hemihydrate and the tetrahydrate, respectively CaSO 3 ·½(H 2 O) and CaSO 3 ·4(H 2 O). [2] All forms are white solids. It is most notable as the product of flue-gas desulfurization.