Calcium Sulfate

Title: Calcium Sulfate
CAS Registry Number: 7778-18-9
Molecular Formula: CaO4S
Molecular Weight: 136.14
Percent Composition: Ca 29.44%, O 47.01%, S 23.55%
Line Formula: CaSO4
Literature References: Review: R. J. Wenk, P. L. Henkels in Kirk-Othmer Encyclopedia of Chemical Technology vol. 4 (Wiley-Interscience, New York, 3rd ed., 1978) pp 437-448.
Properties: The natural form of anhydrous calcium sulfate is known as the mineral anhydrite; also as karstenite, muriacite, anhydrous sulfate of lime, anhydrous gypsum. Crystals are orthorhombic, color varies, e.g., white with blue, gray or reddish tinge, or brick red. d 2.96. Hardness 3-3.5 (Mohs'). Sol in water (18.75°) 0.2 pts/100 pts. Insoluble anhydrite or dead-burned gypsum which has the same crystal structure as the mineral is obtained upon complete dehydration of gypsum at above 650°. Soluble anhydrite is obtained in granular or powder form by complete dehydration of gypsum at below 300° in an electric oven. Estimated pore space is 38% by volume. Possesses high affinity for water and will absorb 6.6% of its weight of water forming the stable hemihydrate.
Density: d 2.96
Derivative Type: Hemihydrate
CAS Registry Number: 26499-65-0
Additional Names: Dried calcium sulfate; dried gypsum; plaster of Paris
Trademarks: Annalin
Properties: Fine, odorless, tasteless powder. When mixed with water, sets to a hard mass. Keep well closed.
Derivative Type: Dihydrate
CAS Registry Number: 13397-24-5
Additional Names: Native calcium sulfate; precipitated calcium sulfate; gypsum; alabaster; selenite; terra alba; satinite; mineral white; satin spar; light spar
Properties: Lumps or powder. d 2.32. It loses only part of its water at 100-150°. Sol in water; very slowly sol in glycerol. Practically insol in most organic solvents.
Density: d 2.32
CAUTION: Potential symptoms of overexposure to anhydrous compd, dihydrate or hemihydrate are irritation of eyes, skin, mucous membranes, respiratory system; cough. Potential symptoms of overexposure to anhydrous compd also include conjunctivitis; rhinitis, epistaxis. Potential symptoms of overexposure to dihydrate also include sneezing, rhinorrhea. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) pp 48, 154, 260.
Use: Anhydrous: Insol anhydrite is used in cement formulations and as a paper filler. Soluble anhydride, because of its strong tendency to absorb moisture, is useful as a drying agent for solids, organic liquids and gases; the desiccant used in laboratory and industry is known under the name Drierite. This material can be regenerated repeatedly and reused without noticeable decrease in its desiccating efficiency. The hemihydrate is used for wall plasters; wallboard; tiles and blocks for the building industry; moldings; statuary; in the paper industry. The dihydrate is used in the manuf of portland cement; in soil treatment to neutralize alkali carbonates and to prevent loss of volatile and dissolved nitrogenous compounds by volatilization and leaching; for the manuf of plaster of Paris, artificial marble; as a white pigment, filler or glaze in paints, enamels, pharmaceuticals, paper, insecticide dusts, yeast manuf, water treatment, polishing powders; in the manuf of sulfuric acid, CaC2, (NH4)2SO4, porous polymers. Pharmaceutic aid (in plaster casts).
Calcium Sulfide Calcium Sulfite Calcium Tartrate Calcium Thiocyanate Calcium Thioglycollate

Calcium sulfate
Calcium sulfate hemihydrate
CAS number 7778-18-9 YesY
10034-76-1 (hemihydrate),
10101-41-4 (dihydrate)
PubChem 24928
ChemSpider 22905 YesY
UNII E934B3V59H YesY
KEGG D09201 N
ChEBI CHEBI:31346 YesY
RTECS number WS6920000
Jmol-3D images Image 1
Molecular formula CaSO4
Molar mass 136.14 g/mol (anhydrous)
145.15 g/mol (hemihydrate)
172.172 g/mol (dihydrate)
Appearance white solid
Odor odorless
Density 2.96 g/cm3 (anhydrous)
2.32 g/cm3 (dihydrate)
Melting point 1460 °C (anhydrous)
Solubility in water 0.21g/100ml at 20 °C (anhydrous)[2]
0.24 g/100ml at 20 °C (dihydrate)[3]
Solubility product, Ksp 4.93 × 10−5 mol2L−2 (anhydrous)
3.14 × 10−5 (dihydrate)
Solubility in glycerol slightly soluble (dihydrate)
Acidity (pKa) 10.4 (anhydrous)
7.3 (dihydrate)
Crystal structure orthorhombic
Std molar
entropy So298
107 J·mol−1·K−1 [4]
Std enthalpy of
formation ΔfHo298
-1433 kJ/mol[4]
MSDS External MSDS
EU Index Not listed
NFPA 704
NFPA 704.svg
Flash point Non-flammable
Related compounds
Other cations Magnesium sulfate
Strontium sulfate
Barium sulfate
Related desiccants Calcium chloride
Magnesium sulfate
Related compounds Plaster of Paris
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Calcium sulfate (or calcium sulphate) is a common laboratory and industrial chemical. In the form of γ-anhydrite (the nearly anhydrous form), it is used as a desiccant. It is also used as a coagulant in products like tofu.[5] In the natural state, unrefined calcium sulfate is a translucent, crystalline white rock. When sold as a color-indicating variant under the name Drierite, it appears blue or pink due to impregnation with Cobalt(II) chloride, which functions as a moisture indicator. The hemihydrate (CaSO4·~0.5H2O) is better known as plaster of Paris, while the dihydrate (CaSO4·2H2O) occurs naturally as gypsum. The anhydrous form occurs naturally as β-anhydrite. Depending on the method of calcination of calcium sulfate dihydrate, specific hemihydrates are sometimes distinguished: alpha-hemihydrate and beta-hemihydrate.[6] They appear to differ only in crystal size. Alpha-hemihydrate crystals are more prismatic than beta-hemihydrate crystals and, when mixed with water, form a much stronger and harder superstructure.[7]