View source for Calcium hydroxide

{{chembox
| verifiedrevid = 322030891
| Name = Calcium hydroxide
| ImageFile = Calcium hydroxide.jpg
| ImageSize = 200px
| ImageName = Calcium hydroxide
| IUPACName = Calcium hydroxide
| OtherNames = Slaked lime<br/>Milk of lime<br/>Calcium(II) hydroxide<br/>Pickling lime
| Section1 = {{Chembox Identifiers
| ChemSpiderID = 14094
| InChI = 1/Ca.2H2O/h;2*1H2/q+2;;/p-2
| SMILES = [Ca+2].[OH-].[OH-]
| InChIKey = AXCZMVOFGPJBDE-NUQVWONBAD
| CASNo = 1305-62-0
| CASNo_Ref = {{cascite}}
| PubChem = 14777
| EINECS = 215-137-3
| RTECS = EW2800000
 }}
| Section2 = {{Chembox Properties
| Formula = Ca(OH)<sub>2</sub>
| MolarMass = 74.093 g/mol
| Appearance = soft white powder/colourless liquid
| Odor = odorless
| Density = 2.211 g/cm<sup>3</sup>, solid
| Solubility = 0.189 g/100 mL (0 °C) <br> 0.173 g/100 mL (20 °C) 
| SolubilityProduct = 4.68{{e|&minus;6}}
| SolubleOther = Soluble in [[glycerol]] and [[acids]]. </br> Insoluble in [[alcohol]].
| MeltingPt = 580 °C <ref>{{cite web| url = http://www.alfa.com/content/msds/USA/14662.pdf| title = MSDS of Calcium hydroxide| accessdate = 2010-09-15}}</ref>
| pKb = 2.37
 }}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc04/icsc0408.htm ICSC 0408]
| EUIndex = Corrosive ('''C'''), Irritant ('''Xi''')
| RPhrases = {{R22}}, {{R34}}
| SPhrases = {{S2}}, {{S24}}
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 0
| NFPA-O = 
| FlashPt = Non-flammable
| LD50 = 7340 mg/kg (oral, rat) </br> 7300 mg/kg (mouse)
 }}
| Section8 = {{Chembox Related
| OtherAnions = 
| OtherCations = [[Magnesium hydroxide]]<br/>[[Strontium hydroxide]]<br/>[[Barium hydroxide]]
| Function = [[base (chemistry)|base]]s
| OtherFunctn = [[Calcium oxide]]
 }}
}}

'''Calcium hydroxide''', traditionally called '''slaked lime''', is an [[inorganic compound]] with the chemical formula [[Calcium|Ca]]([[Hydroxide|OH]])<sub>2</sub>. It is a colourless crystal or white powder and is obtained when [[calcium oxide]] (called ''lime'' or ''quicklime'') is mixed, or "[[wiktionary:slake|slaked]]" with [[water]]. It has many names including '''hydrated lime''', '''builders lime''', '''slack lime''', '''cal''', or '''pickling lime'''.  It is of low toxicity and enjoys many applications.

==Properties===
When heated to 512 °C, the [[partial pressure]] of water in equilibrium with calcium hydroxide reaches 101 kPa that [[chemical decomposition|decomposes]] calcium hydroxide into calcium oxide and water.<ref>{{cite journal | last=Halstead | first=P.E. | coauthors=Moore, A.E.|title=The Thermal Dissociation Of Calcium Hydroxide | journal=Journal of the Chemical Society | volume=769 | pages=3873|year=1957|doi=10.1039/JR9570003873}}</ref> 
:Ca(OH)<sub>2</sub>   →   CaO  + H<sub>2</sub>O
A suspension of fine calcium hydroxide particles in water is called milk of lime. The solution is called [[lime water]] and is a medium strength [[basic (chemistry)|base]] that reacts with [[acid]]s and attacks many [[metal]]s in presence of water. Lime water turns milky in the presence of [[carbon dioxide]] due to formation of [[calcium carbonate]]:
:Ca(OH)<sub>2</sub>   CO<sub>2</sub>   →   CaCO<sub>3</sub>  + H<sub>2</sub>O

Calcium hydroxide is a polymer.  It crystallizes in the same motif as [[cadmium iodide]].  The layers are interconnected by [[hydrogen bond]]s.

==Preparation and occurrence==
Calcium hydroxide is produced commercially by treating lime with water:
:CaO + H<sub>2</sub>O → Ca(OH)<sub>2</sub>

In the laboratory it can be prepared by mixing an [[wiktionary:aqueous|aqueous]] solutions of [[calcium chloride]] and [[sodium hydroxide]]. The mineral form is [[portlandite]] is a relatively rare but found in some volcanic, plutonic, and metamorphic rocks. It has also been known to arise in burning coal dumps.

==Uses==
The largest applicat [[Flocculation|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.  The application enabled by the low cost and non-toxicity of calcium hydroxide.

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]].<ref>Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.</ref>
===Niche uses===
Because of it is produced on a large scale, is easily handled, and is cheap, myriad niche and even large scale applications have been described.  A partial listing follows:
* An ingredient in [[whitewash]], [[mortar (masonry)|mortar]], and [[plaster]]
* It has been proposed to add it to sea water in great quantities to reduce atmospheric [[Carbon dioxide|CO<sub>2</sub>]] and fight the [[greenhouse effect]][http://www.physorg.com/news135820173.html]. However, since the production of calcium oxide (the main starting material of calcium hydroxide) involves [[calcination]] of [[limestone]], which involves great deal of heat, it would be not very productive if fossil fuel were used in the production process. 
* In the production of metals, lime is injected into the waste gas stream to neutralize acids, such as fluorides and chlorides prior to being released to atmosphere.
* An [[alkali]] used as a [[sodium hydroxide|lye]] substitute in no-lye hair [[relaxer]]s
* A [[chemical depilatory]] agent found in Nair
* In [[Bordeaux mixture]] to neutralize the solution and form a long lasting fungicide 
* In the [[oil industry|petroleum refining industry]] for the manufacture of [[additive]]s to [[crude oil|oil]]s (salicatic, sulphatic, fenatic)
* In the chemical industry for manufacture of calcium [[stearic acid|stearate]]
** In the [[petrochemical]] industry for manufacturing solid oil of various marks
** In the manufacture of [[brake|brake pad]]s
** In manufacturing the trademarked compound "Polikar", an [[antifungal]] and [[antimicrobial]] preservative for [[vegetable]]s in storage
** For preparation of dry mixes for [[paint]]ing and decorating
** In manufacturing mixes for [[pesticide]]s
** In the manufacture of [[ebonite]]
===Food hobby and industry===
Because of its low toxicity and the mildness of its basic properties, it is widely used in the In the [[food industry] and associated hobbies: Examples:
**The separation of sugar from sugar cane in the sugar industry
** for processing water for alcoholic beverages, soft drinks.
** Used in the processing of Norwegian [[lutefisk]]. Dried cod fish is soaked in a mixture of slaked lime and soda to produce a soft-fleshed fish fillet that is steamed or baked and served with potato lefse
** home food preservation in the making of [[pickles]].
** clearing a [[brine]] of [[carbonates]] of calcium and [[magnesium]] in the manufacture of salt for food and pharmacopoeia
** In Chinese cuisine, for making [[century eggs]]
** Used to fortify fruit drinks such as Tropicana Calcium + Vitamin D orange juice.
** A calcium supplement in mineral fortified baby formulas
====Native American uses====
In [[Indigenous peoples of the Americas|Native American]] and [[Mesoamerican]] cooking, calcium hydroxide is called "cal". Corn cooked with cal becomes [[Nixtamalization|nixtamal]] which significantly increases the bioavailability of niacin, and is also considered tastier and easier to digest. In chewing [[betel nut]] or [[coca leaves]], calcium hydroxide is usually chewed alongside to keep the [[alkaloid]] [[stimulant]]s chemically available for [[absorption (small intestine)|absorption]] by the body.  Similarly, Native Americans traditionally chewed tobacco leaves with calcium hydroxide derived from burnt shells to enhance the effects.

==Health risks==
As with many chemicals, exposure may pose health risks and exposure should be limited.  Consult the [[MSDS]].<ref>{{cite web| url = http://www.jtbaker.com/msds/englishhtml/c0407.htm| title = MSDS Calcium hydroxide| accessdate = 2008-12-26}}</ref>

==See also==
*[[Lime plaster]]
*[[Lime mortar]]
*[[Plaster]]

==References==
{{Reflist}}

==External links==
* {{cite paper | author=National Organic Standards Board Technical Advisory Panel | title=NOSB TAP Review: Calcium Hydroxid | version= | format=.PDF | publisher=Organic Materials Review Institute | url=http://www.omri.org/CaOH_final.pdf | date=2002-04-04 | accessdate=2008-02-05}}
* [http://www.physchem.ox.ac.uk/MSDS/CA/calcium_hydroxide.html MSDS Data Sheet]
* [http://www.carmeuse.com/page.asp?langue=EN&id=12 Lime production process]

{{Calcium compounds}}

[[Category:Building materials]]
[[Category:Calcium compounds]]
[[Category:Dental materials]]
[[Category:Hydroxides]]
[[Category:Inorganic compounds]]

[[ar:هيدروكسيد الكالسيوم]]
[[bg:Калциев дихидроксид]]
[[ca:Hidròxid de calci]]
[[cs:Hydroxid vápenatý]]
[[da:Læsket kalk]]
[[de:Calciumhydroxid]]
[[et:Kaltsiumhüdroksiid]]
[[es:Hidróxido de calcio]]
[[eo:Kalcia hidroksido]]
[[fa:کلسیم هیدروکسید]]
[[fr:Hydroxyde de calcium]]
[[gl:Hidróxido de calcio]]
[[ko:수산화 칼슘]]
[[id:Kalsium hidroksida]]
[[it:Idrossido di calcio]]
[[lv:Kalcija hidroksīds]]
[[lt:Kalcio hidroksidas]]
[[hu:Kalcium-hidroxid]]
[[ms:Kalsium hidroksida]]
[[nl:Calciumhydroxide]]
[[ja:水酸化カルシウム]]
[[no:Kalsiumhydroksid]]
[[pl:Wodorotlenek wapnia]]
[[pt:Hidróxido de cálcio]]
[[ro:Hidroxid de calciu]]
[[ru:Гидроксид кальция]]
[[simple:Calcium hydroxide]]
[[sk:Hydroxid vápenatý]]
[[fi:Kalsiumhydroksidi]]
[[sv:Kalciumhydroxid]]
[[tl:Calcium hydroxide]]
[[tr:Kalsiyum hidroksit]]
[[uk:Гідроксид кальцію]]
[[vi:Canxi hiđroxit]]
[[zh:氢氧化钙]]
[[Category:2Fix]]