Manufacture of lime and gypsum
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. 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 (CaSO
4·~0.5H
2O) is better known as
plaster of Paris, while the
dihydrate (CaSO
4·2H
2O) 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. 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
| Calcium sulfate |
 |
|
|
| Identifiers |
| CAS number |
7778-18-9,
10034-76-1 (hemihydrate),
10101-41-4 (dihydrate) |
| PubChem |
24928 |
| ChemSpider |
22905 |
| UNII |
E934B3V59H |
| RTECS number |
WS6920000 |
|
|
InChI=1S/Ca.H2O4S/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2
Key: OSGAYBCDTDRGGQ-UHFFFAOYSA-L
InChI=1/Ca.H2O4S/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2
Key: OSGAYBCDTDRGGQ-NUQVWONBAU |
| Properties |
| 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/cm (anhydrous)
2.32 g/cm (dihydrate) |
| Melting point |
1460 °C (anhydrous) |
| Solubility in water |
2.1 g/L (20 °C, anhydrous)
2.4 g/L (20 °C, dihydrate) |
| Solubility product, Ksp |
2.4 × 10 (dihydrate) |
| Solubility in glycerol |
slightly soluble (dihydrate) |
| Acidity (pKa) |
10.4 (anhydrous)
7.3 (dihydrate) |
| Structure |
| Crystal structure |
orthorhombic |
| Thermochemistry |
Std enthalpy of
formation ΔfH298 |
-1434.5 kJ/mol |
| Hazards |
| MSDS |
External MSDS |
| EU Index |
Not listed |
| 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
Gypsum |
| Supplementary data page |
Structure and
properties |
n, εr, etc. |
Thermodynamic
data |
Phase behaviour
Solid, liquid, gas |
| Spectral data |
UV, IR, NMR, MS |
 Y(what is this?) (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
| Infobox references |
From Wikipedia, the free encyclopedia :
Manufacture of lime and gypsum
