出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/05/19 23:12:33」(JST)
| Names | |
|---|---|
| IUPAC name
Calcium hydroxide
|
|
| Other names
Slaked lime
Milk of lime |
|
| Identifiers | |
|
CAS Registry Number
|
1305-62-0 Y |
| ChEBI | CHEBI:31341 Y |
| ChemSpider | 14094 Y |
| EC number | 215-137-3 |
|
InChI
|
|
| Jmol-3D images | Image Image |
| KEGG | D01083 Y |
| PubChem | 14777 |
| RTECS number | EW2800000 |
|
SMILES
|
|
| UNII | PF5DZW74VN Y |
| 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
|
0.189 g/100 mL (0 °C) 0.173 g/100 mL (20 °C) |
|
Solubility product (Ksp)
|
5.5×10−6 |
| Solubility | Soluble in glycerol and acids. Insoluble in alcohol. |
| Acidity (pKa) | 12.4 |
| Basicity (pKb) | 2.37 |
|
Refractive index (nD)
|
1.574 |
| Thermochemistry | |
|
Std molar
entropy (S |
83 J·mol−1·K−1[1] |
|
Std enthalpy of
formation (ΔfH |
−987 kJ·mol−1[1] |
| Hazards | |
| MSDS | External MSDS |
| EU Index | C (C), Xi (Xi) |
| R-phrases | R22, R34 |
| S-phrases | (S2), S24 |
| NFPA 704 |
0
3
0
|
| Flash point | Non-flammable |
|
LD50 (Median lethal 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)[3] |
|
REL (Recommended)
|
TWA 5 mg/m3[3] |
|
IDLH (Immediate danger)
|
N.D.[3] |
| Related compounds | |
|
Other cations
|
Magnesium hydroxide Strontium hydroxide |
|
Related bases
|
Calcium oxide |
| Supplementary data page | |
|
Structure and
properties |
Refractive index (n), Dielectric constant (εr), etc. |
|
Thermodynamic
data |
Phase behaviour solid–liquid–gas |
|
Spectral data
|
UV, IR, NMR, MS |
|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|
|
| Y verify (what is: Y/N?) | |
| 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 "slaked" with water. It has many names including hydrated 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.
When heated to 512 °C, the partial pressure of water in equilibrium with calcium hydroxide reaches 101 kPa (normal atmospheric pressure), which decomposes calcium hydroxide into calcium oxide and water.[4]
A suspension of fine calcium hydroxide particles in water is called milk of lime. The solution is called limewater and is a medium strength base that reacts with acids and attacks many metals. Limewater turns milky in the presence of carbon dioxide due to formation of calcium carbonate, a process called carbonatation:
Calcium hydroxide adopts a polymeric structure, as do the related hydroxides of the alkaline earth metals. The packing resembles the cadmium iodide motif with layers of octahedral Ca centres. Strong hydrogen bonds exist between the layers.[5]
Calcium hydroxide is produced commercially by treating lime with water:
In the laboratory it can be prepared by mixing aqueous solutions of calcium chloride and sodium hydroxide. The mineral form, portlandite, is relatively rare but can be found in some volcanic, plutonic, and metamorphic rocks. It has also been known to arise in burning coal dumps.
One significant application of calcium hydroxide is as a flocculant, in water and sewage treatment. It forms a fluffy charged solid that aids in the removal of smaller particles from water, resulting in a clearer product. This application is enabled by the low cost and low toxicity of calcium hydroxide. It is also used in fresh water treatment for raising the pH of the water so pipes will not corrode where the base water is acidic because it is self-regulating and does not raise the pH too much.
Another large application is in the paper industry, where it is used in the production of sodium hydroxide. This conversion is a component of the Kraft process.[5]
Calcium hydroxide is produced on a large scale, is easily handled and is generally inexpensive. Numerous niche applications are in use. A partial listing follows:
According to Diodorus Siculus:
"The Gauls are tall of body with rippling muscles and white of skin and their hair is blond, and not only naturally so for they also make it their practice by artificial means to increase the distinguishing colour which nature has given it. For they are always washing their hair in limewater and they pull it back from the forehead to the nape of the neck, with the result that their appearance is like that of Satyrs and Pans since the treatment of their hair makes it so heavy and coarse that it differs in no respect from the mane of horses."
Because of its low toxicity and the mildness of its basic properties, slaked lime is widely used in the food industry to:
In Spanish, calcium hydroxide is called cal. Corn cooked with cal (nixtamalization) becomes hominy (nixtamal), which significantly increases the bioavailability of niacin, and it is also considered tastier and easier to digest.
In chewing areca nut or coca leaves, calcium hydroxide is usually chewed alongside to keep the alkaloid stimulants chemically available for absorption by the body. Similarly, Native Americans traditionally chewed tobacco leaves with calcium hydroxide derived from burnt mollusk shells to enhance the effects. It has also been used by some indigenous American tribes as an ingredient in yopo, a psychedelic snuff prepared from the beans of some Anadenanthera species.[7]
It is used in making naswar (also known as nass or niswar), a type of dipping tobacco made from fresh tobacco leaves, calcium hydroxide (chuna), and wood ash. It is consumed most in the Pathan diaspora, Afghanistan, Pakistan, India, Bangladesh and also in Sweden and Norway. Villagers also use calcium hydroxide to paint their mud houses in Afghanistan and Pakistan.
Unprotected exposure to Ca(OH)2 can pose health risks, so it should be limited. It can cause severe skin irritation, chemical burns, blindness, or lung damage. See MSDS.[2]
|
||||||
|
||||||
全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.
| 関連記事 | 「hydroxide」「calcium」 |