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Hydrated lime

Calcium hydroxide
Calcium hydroxide
Mg(OH)2Xray.jpg
Names
IUPAC name
Calcium hydroxide
Other names
Slaked lime
Milk of lime
Caustic lime
Calcium(II) hydroxide
Pickling lime
Hydrated lime
Portlandite
Calcium hydrate
Identifiers
1305-62-0 YesY
3D model (Jmol) Interactive image
Interactive image
ChEBI CHEBI:31341 YesY
ChemSpider 14094 YesY
ECHA InfoCard 100.013.762
EC Number 215-137-3
E number E526 (acidity regulators, ...)
846915
KEGG D01083 YesY
PubChem 14777
RTECS number EW2800000
UNII PF5DZW74VN YesY
Properties
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)
1.89 g/L (0 °C)
1.73 g/L (20 °C)
0.66 g/L (100 °C)
5.5×10−6
Solubility Soluble in glycerol and acids.
Insoluble in alcohol.
Basicity (pKb) 1.37 (first OH), 2.43 (second OH)
-22.0·10−6 cm3/mol
1.574
Structure
Hexagonal, hP3
P3m1 No. 164
a = 0.35853 nm, c = 0.4895 nm
Thermochemistry
83 J·mol−1·K−1
−987 kJ·mol−1
Hazards
Safety data sheet See: data page
R-phrases R22, R34
S-phrases (S2), S24
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)
7340 mg/kg (oral, rat)
7300 mg/kg (mouse)
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 15 mg/m3 (total) 5 mg/m3 (resp)
REL (Recommended)
TWA 5 mg/m3
IDLH (Immediate danger)
N.D.
Related compounds
Other cations
Magnesium hydroxide
Strontium hydroxide
Barium hydroxide
Related bases
Calcium oxide
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Thermodynamic
data
Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY  (what is YesYN ?)
Infobox references

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 obtained when calcium oxide (called lime or quicklime) is mixed, or "" with water. It has many names including hydrated lime, caustic lime, builders' lime, slack lime, cal, or pickling lime. Calcium hydroxide is used in many applications, including food preparation. Limewater is the common name for a saturated solution of calcium hydroxide.

Calcium hydroxide is relatively insoluble in water, with a solubility product Ksp of 5.5 × 10−6. It is large enough that its solutions are basic according to the following reaction:

At ambient temperature, calcium hydroxide (portlandite) dissolves in pure water to produce an alkaline solution with a pH of about 12.4. Calcium hydroxide solutions can cause chemical burns. At high pH value (see common ion effect), its solubility drastically decreases. This behavior is relevant to cement pastes. Its aqueous solutions is called limewater and is a medium strength base that reacts with acids and can attack some metals such as aluminium (amphoteric hydroxide dissolving at high pH) while protecting other metals from corrosion such as iron and steel by passivation of their surface. Limewater turns milky in the presence of carbon dioxide due to formation of calcium carbonate, a process called carbonatation:


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