| 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 |
| 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 |
| 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 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. Calcium hydroxide is used in many applications, including food preparation.
Contents |
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.[2]
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:
Calcium hydroxide crystallizes in the same motif as cadmium iodide. The layers are interconnected by hydrogen bonds.
Calcium hydroxide is produced commercially by treating lime with water:
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.
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 won't corrode where the base water is acidic because it's 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.[3]
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:
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.
Because of its low toxicity and the mildness of its basic properties, it is widely used in the food industry and associated hobbies: Examples:
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.[5]
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.
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.[1]
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