Calcium hydroxide

Calcium hydroxide
Calcium hydroxide
IUPAC name Calcium hydroxide
Other names Slaked lime Milk of lime Calcium(II) hydroxide Pickling lime
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	1305-62-0 Y
PubChem	14777
ChemSpider	14094
EC number	215-137-3
RTECS number	EW2800000
SMILES
InChI
InChI key	AXCZMVOFGPJBDE-NUQVWONBAD
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula	Ca(OH)2
Molar mass	74.093 g/mol
Appearance	soft white powder/colourless liquid
Odor	odorless
Density	2.211 g/cm3, solid
Melting point	580 °C
Solubility in water	0.189 g/100 mL (0 °C) 0.173 g/100 mL (20 °C)
Solubility product, Ksp	4.68 × 10−6
Solubility	Soluble in glycerol and acids. Insoluble in alcohol.
Basicity (pKb)	2.37
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
MSDS	ICSC 0408
EU Index	Corrosive (C), Irritant (Xi)
R-phrases	R22, R34
S-phrases	(S2), S24
NFPA 704	75px 0 3 0
Flash point	Non-flammable
LD50	7340 mg/kg (oral, rat) 7300 mg/kg (mouse)
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Other cations	Magnesium hydroxide Strontium hydroxide Barium hydroxide
Related bases	Calcium oxide
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

Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca(OH)₂. It is a colourless 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. 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 decomposes calcium hydroxide into calcium oxide and water.

Ca(OH)₂ → CaO + H₂O

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 base that reacts with acids and attacks many metals in presence of water. Lime water turns milky in the presence of carbon dioxide due to formation of calcium carbonate:

Ca(OH)₂ CO₂ → CaCO₃ + H₂O

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

Preparation and occurrence

Calcium hydroxide is produced commercially by treating lime with water:

CaO + H₂O → Ca(OH)₂

In the laboratory it can be prepared by mixing an 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 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.

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, and plaster
• It has been proposed to add it to sea water in great quantities to reduce atmospheric CO₂ and fight the greenhouse effect[1]. 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 lye substitute in no-lye hair relaxers
• A chemical depilatory agent found in Nair
• In Bordeaux mixture to neutralize the solution and form a long lasting fungicide
• In the petroleum refining industry for the manufacture of additives to oils (salicatic, sulphatic, fenatic)
• In the chemical industry for manufacture of calcium stearate
  • In the petrochemical industry for manufacturing solid oil of various marks
  • In the manufacture of brake pads
  • In manufacturing the trademarked compound "Polikar", an antifungal and antimicrobial preservative for vegetables in storage
  • For preparation of dry mixes for painting and decorating
  • In manufacturing mixes for pesticides
  • 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 Native American and Mesoamerican cooking, calcium hydroxide is called "cal". Corn cooked with cal becomes 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 stimulants chemically available for 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.

See also

• Lime plaster
• Lime mortar
• Plaster

External links

• National Organic Standards Board Technical Advisory Panel (2002-04-04). "NOSB TAP Review: Calcium Hydroxid" (.PDF). Organic Materials Review Institute. Retrieved 2008-02-05. 
• MSDS Data Sheet
• Lime production process

ar:هيدروكسيد الكالسيوم zh:氢氧化钙