Calcium hydroxide
| Calcium hydroxide | |
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Calcium hydroxide |
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Other names
Slaked lime |
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| Identifiers | |
| CAS number | 1305-62-0  |
| PubChem | 14777 |
| ChemSpider | 14094 |
| UNII | PF5DZW74VN |
| EC number | 215-137-3 |
| KEGG | D01083 |
| ChEBI | CHEBI:31341 |
| RTECS number | EW2800000 |
| Jmol-3D images | Image 1 Image 2 |
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| Properties | |
| Molecular formula | Ca(OH)2 |
| Molar mass | 74.093 g/mol |
| Exact mass | 73.968071 |
| Appearance | soft white powder/colourless liquid |
| Odor | odorless |
| Density | 2.211 g/cm3, solid |
| Melting point |
580 °C (loses water) |
| Solubility in water | 0.189 g/100 mL (0 °C) 0.173 g/100 mL (20 °C) 0.066 g/100 mL (100 °C) |
| Solubility product, Ksp | 4.68×10−6 |
| Solubility | Soluble in glycerol and acids. Insoluble in alcohol. |
| Acidity (pKa) | 12.4 |
| Basicity (pKb) | 2.37 |
| Refractive index (nD) | 1.574 |
| Thermochemistry | |
| Std enthalpy of formation ΔfH |
−987 kJ·mol−1[1] |
| Standard molar entropy S |
83 J·mol−1·K−1[1] |
| Hazards | |
| MSDS | External MSDS |
| EU Index | Corrosive (C), Irritant (Xi) |
| R-phrases | R22, R34 |
| S-phrases | (S2), S24 |
| NFPA 704 |
 0
3
0
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| Flash point | Non-flammable |
| LD50 | 7340 mg/kg (oral, rat) 7300 mg/kg (mouse) |
| Related compounds | |
| Other cations | Magnesium hydroxide Strontium hydroxide Barium hydroxide |
| Related bases | Calcium oxide |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| 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. It is of low toxicity. Calcium hydroxide is used in many applications, including food preparation.
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[edit] Properties
When heated to 512 °C, the partial pressure of water in equilibrium with calcium hydroxide reaches 101 kPa, which decomposes calcium hydroxide into calcium oxide and water.[3]
- 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. Lime water turns milky in the presence of carbon dioxide due to formation of calcium carbonate:
- Ca(OH)2 + CO2 → CaCO3 + H2O
Calcium hydroxide crystallizes in the same motif as cadmium iodide. The layers are interconnected by hydrogen bonds.
[edit] 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, 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.
[edit] Uses
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 non-toxicity of calcium hydroxide. It is also used in fresh water treatment for raising the pH of the water so that the 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.[4]
[edit] Niche uses
Because 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:
- In life support systems as a carbon dioxide scrubber, particularly in closed-circuit diving re-breathers such as the US Navy LAR V or MK-16, where the more caustic Lithium Hydroxide is deemed too risky due to inhaled dust, combat handling, or generation of caustic "slurry" in flooding events
- An ingredient in whitewash, mortar, and plaster
- To fill the root canal for the first stage of endodontic therapy (it is then replaced by rubber).
- As an additive to sea water to reduce atmospheric CO2 and mitigate the greenhouse effect.[5]
- 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 most hair removal creams (for example Nair)
- In Bordeaux mixture to neutralize the solution and form a long lasting fungicide
- In lime-sulfur it is mixed with sulfur and boiled in water for an hour. The ratio by weight of Ca(OH)2:S:water is about 1:1.7:8.7. Diluted (1:32) lime-sulfur is sprayed as a fungicide and used as a dip to combat sarcoptic mange.
- 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
- As a calcium supplement and pH/carbonate buffer (known as Kalkwasser) for the aquaculture of corals in reef aquaria.
- As a natural "alternative" insecticide. Most crawling insects are killed by its touch. Including: ticks, fleas, beetles and grubs.
For making a fungicide or a dip for treating mange it is boiled with sulfur, then diluted. One recipe for the concentrate is 36 lb quicklime, 80 lb sulfur, and 50 gal water boiled for 1 hour—the authors suggesting 1/3 more lime if slaked lime is used.
[edit] Food industry
Because of its low toxicity and the mildness of its basic properties, it is widely used in the food industry and associated hobbies: Examples:
- The separation of sugar from sugar cane or sugar beets in the sugar industry, see carbonatation
- For processing water for alcoholic beverages, soft drinks.
- Used in the processing of Norwegian lutefisk.[citation needed] 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 infant formula
- A condiment used mainly in Bengali families, predominantly the men, when they take areca nuts, calcium hydroxide and a variety of other seeds wrapped in betel leaves. They call this "paan"
- Use as alternative ingredient to baking soda (raising agent) in papadam. (South Indian flatbread)
[edit] 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 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 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.[6]
[edit] Afghan uses
Used in making naswar (also known as nass or niswar) is a type of dipping tobacco, made from fresh tobacco leaves, calcium hydroxide (Chuna), and wood ash. calcium oxide plays an important role in making a naswar. It is consumed most in the Pathan diaspora, Afghanistan, Pakistan, India and also in Sweden, Norway. Villagers also use calcium hydroxide as a paint on to their mud made houses all over Afghanistan and Pakistan.
[edit] Health risks
Unprotected exposure can pose health risks and exposure should be limited. It can cause severe skin irritation and chemical burns/ blindness/ lung damage. See MSDS.[2]
[edit] See also
[edit] References
- ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed.. Houghton Mifflin Company. p. A21. ISBN 061894690X.
- ^ a b "MSDS Calcium hydroxide". http://www.avantormaterials.com/documents/MSDS/usa/English/C0407_msds_us_Default.pdf. Retrieved 2011-06-21.
- ^ Halstead, P.E.; Moore, A.E. (1957). "The Thermal Dissociation Of Calcium Hydroxide". Journal of the Chemical Society 769: 3873. doi:10.1039/JR9570003873.
- ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
- ^ O,Driscoll, Catherine (21 July 2008). "A dash of lime -- a new twist that may cut CO2 levels back to pre-industrial levels". Chemistry. PhysOrg.com. http://www.physorg.com/news135820173.html. Retrieved 20 November 2010.
- ^ A multidisciplinary overview of intoxicating snuff rituals in the western hemisphere, Peter A. G. M. de Smet, doi:10.1016/0378-8741(85)90060-1
[edit] External links
- National Organic Standards Board Technical Advisory Panel (2002-04-04) (.PDF). NOSB TAP Review: Calcium Hydroxid. Organic Materials Review Institute. Archived from the original on 2007-10-31. http://web.archive.org/web/20071031101142/http://www.omri.org/CaOH_final.pdf. Retrieved 2008-02-05.
- MSDS Data Sheet
- Lime production process
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