Calcium hydroxide

Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH)₂. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed with water. Annually, approximately 125 million tons of calcium hydroxide are produced worldwide.

Calcium hydroxide

Names
IUPAC name Calcium hydroxide
Other names Slaked lime Milk of lime Calcium(II) hydroxide Pickling lime Hydrated lime Portlandite Calcium hydrate Calcium dihydroxide
Identifiers
CAS Number	1305-62-0 Y
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:31341 Y
ChemSpider	14094 Y
ECHA InfoCard	100.013.762
EC Number	215-13
E number	E526 (acidity regulators, ...)
Gmelin Reference	846915
KEGG	D01083 Y
PubChem CID	14777
RTECS number	EW2800000
UNII	PF5DZW74VN Y
CompTox Dashboard (EPA)	DTXSID7034410
InChI InChI=1S/Ca.2H2O/h;2*1H2/q+2;;/p-2 Y Key: AXCZMVOFGPJBDE-UHFFFAOYSA-L Y InChI=1/Ca.2H2O/h;2*1H2/q+2;;/p-2 Key: AXCZMVOFGPJBDE-NUQVWONBAD
SMILES [Ca+2].[OH-].[OH-] [OH-].[OH-].[Ca+2]
Properties
Chemical formula	Ca(OH)2
Molar mass	74.093 g/mol
Appearance	White powder
Odor	Odorless
Density	2.211 g/cm3, solid
Melting point	580 °C (1,076 °F; 853 K) (loses water, decomposes)
Solubility in water	1.89 g/L (0 °C) 1.73 g/L (20 °C) 0.66 g/L (100 °C) (retrograde solubility, i.e., unusually decreasing with T)
Solubility product (Ksp)	5.02×10−6
Solubility	Soluble in glycerol and acids. Insoluble in ethanol.[citation needed]
Acidity (pKa)	pKa1 = 12.63 pKa2 = 11.57
Magnetic susceptibility (χ)	−22.0·10−6 cm3/mol
Refractive index (nD)	1.574
Structure
Crystal structure	Hexagonal, hP3
Space group	P3m1 No. 164
Lattice constant	a = 0.35853 nm, c = 0.4895 nm
Thermochemistry
Std molar entropy (S⦵298)	83 J·mol−1·K−1
Std enthalpy of formation (ΔfH⦵298)	−987 kJ·mol−1
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H335, H402
Precautionary statements	P261, P280, P305+P351+P338
NFPA 704 (fire diamond)	3 0 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	7340 mg/kg (oral, rat) 7300 mg/kg (mouse)
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 15 mg/m3 (total) 5 mg/m3 (resp.)
REL (Recommended)	TWA 5 mg/m3
IDLH (Immediate danger)	N.D.
Safety data sheet (SDS)
Related compounds
Other cations	Magnesium hydroxide Strontium hydroxide Barium hydroxide
Related bases	Calcium oxide
Supplementary data page
Calcium hydroxide (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Calcium hydroxide has many names including hydrated lime, caustic lime, builders' lime, slaked lime, cal, and pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater, also called milk of lime, is the common name for a saturated solution of calcium hydroxide.