Calcium oxide ( formula : Ca O ), commonly known as quicklime or burnt lime , is a widely used chemical compound . It is a white, caustic , alkaline , crystalline solid at room temperature . The broadly used term lime connotes calcium-containing inorganic compounds , in which carbonates , oxides , and hydroxides of calcium, silicon , magnesium , aluminium , and iron predominate. By contrast, quicklime specifically applies to the single compound calcium oxide. Calcium oxide that survives processing without reacting in building products , such as cement , is called free lime .
31-399: Quicklime is relatively inexpensive. Both it and the chemical derivative calcium hydroxide (of which quicklime is the base anhydride ) are important commodity chemicals. Calcium oxide is usually made by the thermal decomposition of materials, such as limestone or seashells , that contain calcium carbonate (CaCO 3 ; mineral calcite ) in a lime kiln . This is accomplished by heating
62-497: A fire hazard, its reaction with water can release enough heat to ignite combustible materials. Calcium oxide is also a separate mineral species (with the unit formula CaO), named 'Lime'. It has an isometric crystal system , and can form a solid solution series with monteponite . The crystal is brittle, pyrometamorphic, and is unstable in moist air, quickly turning into portlandite (Ca(OH) 2 ). Calcium hydroxide Calcium hydroxide (traditionally called slaked lime )
93-411: A leather process called liming . The ion CaOH has been detected in the atmosphere of S-type stars . Limewater is a saturated aqueous solution of calcium hydroxide. Calcium hydroxide is sparsely soluble at room temperature in water (1.5 g/L at 25 °C ). "Pure" (i.e. less than or fully saturated) limewater is clear and colorless, with a slight earthy smell and an astringent/bitter taste. It
124-456: A process called sulfation , sulphur dioxide reacts with limewater: Limewater is used in a process known as lime softening to reduce water hardness. It is also used as a neutralizing agent in municipal waste water treatment. Calcium hydroxide adopts a polymeric structure, as do all metal hydroxides. The structure is identical to that of Mg(OH) 2 ( brucite structure ); i.e., the cadmium iodide motif. Strong hydrogen bonds exist between
155-580: A process known as nixtamalization . Nixtamalization makes the niacin nutritionally available and prevents pellagra . Traditionally lime water was used in Taiwan and China to preserve persimmon and to remove astringency . In chewing 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 mollusc shells to enhance
186-416: Is a substitute for dolomitic lime as a flux in steelmaking. Because of vigorous reaction of quicklime with water, quicklime causes severe irritation when inhaled or placed in contact with moist skin or eyes. Inhalation may cause coughing, sneezing, and labored breathing. It may then evolve into burns with perforation of the nasal septum, abdominal pain, nausea and vomiting. Although quicklime is not considered
217-481: Is also used in tanning and making parchment . The lime is used as a dehairing agent based on its alkaline properties. Treating one's hair with limewater causes it to stiffen and bleach, with the added benefit of killing any lice or mites living there. Diodorus Siculus described the Celts as follows: "Their aspect is terrifying... They are very tall in stature, with rippling muscles under clear white skin. Their hair
248-428: Is an inorganic compound with the chemical formula Ca ( OH ) 2 . It is a colorless crystal or white powder and is produced when quicklime ( calcium oxide ) is mixed with water . Annually, approximately 125 million tons of calcium hydroxide are produced worldwide. Calcium hydroxide has many names including hydrated lime , caustic lime , builders' lime , slaked lime , cal , and pickling lime . Calcium hydroxide
279-423: Is around 283 million tonnes. China is by far the world's largest producer, with a total of around 170 million tonnes per year. The United States is the next largest, with around 20 million tonnes per year. Approximately 1.8 t of limestone is required per 1.0 t of quicklime. Quicklime has a high affinity for water and is a more efficient desiccant than silica gel . The reaction of quicklime with water
310-406: 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 that pipes will not corrode where the base water is acidic, because it
341-509: Is associated with an increase in volume by a factor of at least 2.5. Hydroxyapatite's free CaO content rises with increased calcination temperatures and longer times. It also pinpoints particular temperature cutoffs and durations that impact the production of CaO, offering information on how calcination parameters impact the composition of the material. In 80 BC, the Roman general Sertorius deployed choking clouds of caustic lime powder to defeat
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#1732790213577372-414: Is basic in nature with a pH of 12.4. Limewater is named after limestone , not the lime fruit . Limewater may be prepared by mixing calcium hydroxide (Ca(OH) 2 ) with water and removing excess undissolved solute (e.g. by filtration). When excess calcium hydroxide is added (or when environmental conditions are altered, e.g. when its temperature is raised sufficiently), there results a milky solution due to
403-407: Is blond, but not only naturally so: they bleach it, to this day, artificially, washing it in lime and combing it back from their foreheads. They look like wood-demons, their hair thick and shaggy like a horse's mane. Some of them are clean-shaven, but others – especially those of high rank, shave their cheeks but leave a moustache that covers the whole mouth...". Calcium hydroxide is also applied in
434-464: Is cooked with nextli to become nixtamal , also known as hominy . Nixtamalization significantly increases the bioavailability of niacin (vitamin B3), and is also considered tastier and easier to digest. Nixtamal is often ground into a flour, known as masa , which is used to make tortillas and tamales. Limewater is used in the preparation of maize for corn tortillas and other culinary purposes using
465-481: Is large enough that its solutions are basic according to the following dissolution reaction: The solubility is affected by the common-ion effect . Its solubility drastically decreases upon addition of hydroxide or calcium sources. 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: When carbon dioxide
496-475: Is not an organic compound . The study of inorganic compounds is a subfield of chemistry known as inorganic chemistry . Inorganic compounds comprise most of the Earth's crust , although the compositions of the deep mantle remain active areas of investigation. All allotropes (structurally different pure forms of an element) and some simple carbon compounds are often considered inorganic. Examples include
527-561: Is passed through limewater, the solution takes on a milky appearance due to precipitation of insoluble calcium carbonate : If excess CO 2 is added: the following reaction takes place: The milkiness disappears since calcium bicarbonate is water-soluble. Calcium hydroxide reacts with aluminium . This reaction is the basis of aerated concrete . It does not corrode iron and steel , owing to passivation of their surface. Calcium hydroxide reacts with hydrochloric acid to give calcium hydroxychloride and then calcium chloride . In
558-518: Is self-regulating and does not raise the pH too much. Another large application is in the paper industry, where it is an intermediate in the reaction in the production of sodium hydroxide. This conversion is part of the causticizing step in the Kraft process for making pulp. In the causticizing operation, burned lime is added to green liquor , which is a solution primarily of sodium carbonate and sodium sulfate produced by dissolving smelt , which
589-437: Is slower to react and may have other disadvantages compared with lime, depending on the application; however, limestone is considerably less expensive than lime. Calcined gypsum is an alternative material in industrial plasters and mortars. Cement, cement kiln dust, fly ash, and lime kiln dust are potential substitutes for some construction uses of lime. Magnesium hydroxide is a substitute for lime in pH control, and magnesium oxide
620-483: Is the molten form of these chemicals from the recovery furnace. In orchard crops, calcium hydroxide is used as a fungicide. Applications of 'lime water' prevent the development of cankers caused by the fungal pathogen Neonectria galligena . The trees are sprayed when they are dormant in winter to prevent toxic burns from the highly reactive calcium hydroxide. This use is authorised in the European Union and
651-426: Is used as the colour solvent to apply on fresh plaster. Historically, it is known as the paint whitewash . Limewater is widely used by marine aquarists as a primary supplement of calcium and alkalinity for reef aquariums. Corals of order Scleractinia build their endoskeletons from aragonite (a polymorph of calcium carbonate). When used for this purpose, limewater is usually referred to as Kalkwasser . It
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#1732790213577682-536: Is used in making naswar (also known as nass or niswar ), a type of dipping tobacco made from fresh tobacco leaves, calcium hydroxide ( chuna / choona or soon ), and wood ash. It is consumed most in the Pathan diaspora, Afghanistan , Pakistan , India and Bangladesh . Villagers also use calcium hydroxide to paint their mud houses in Afghanistan, Pakistan and India. In buon fresco painting, limewater
713-471: Is used in many applications, including food preparation, where it has been identified as E number E526 . Limewater , also called milk of lime , is the common name for a saturated solution of calcium hydroxide. Calcium hydroxide is modestly soluble in water, as seen for many dihydroxides. Its solubility increases from 0.66 g/L at 100 °C to 1.89 g/L at 0 °C. Its solubility product K sp of 5.02 × 10 at 25 °C, its dissociation in water
744-524: The Characitani of Hispania , who had taken refuge in inaccessible caves. A similar dust was used in China to quell an armed peasant revolt in 178 AD, when lime chariots equipped with bellows blew limestone powder into the crowds. Quicklime is also thought to have been a component of Greek fire . Upon contact with water, quicklime would increase its temperature above 150 °C (302 °F) and ignite
775-519: The United Kingdom under Basic Substance regulations. Calcium hydroxide is used in dentistry, primarily in the specialty of endodontics. Because of its low toxicity and the mildness of its basic properties, slaked lime is widely used in the food industry , In Nahuatl , the language of the Aztecs , the word for calcium hydroxide is nextli . In a process called nixtamalization , maize
806-541: The allotropes of carbon ( graphite , diamond , buckminsterfullerene , graphene , etc.), carbon monoxide CO , carbon dioxide CO 2 , carbides , and salts of inorganic anions such as carbonates , cyanides , cyanates , thiocyanates , isothiocyanates , etc. Many of these are normal parts of mostly organic systems, including organisms ; describing a chemical as inorganic does not necessarily mean that it cannot occur within living things. Friedrich Wöhler 's conversion of ammonium cyanate into urea in 1828
837-400: The effects. It has also been used by some indigenous South American tribes as an ingredient in yopo , a psychedelic snuff prepared from the beans of some Anadenanthera species. Calcium hydroxide is typically added to a bundle of areca nut and betel leaf called " paan " to keep the alkaloid stimulants chemically available to enter the bloodstream via sublingual absorption. It
868-548: The fuel. David Hume , in his History of England , recounts that early in the reign of Henry III , the English Navy destroyed an invading French fleet by blinding the enemy fleet with quicklime. Quicklime may have been used in medieval naval warfare – up to the use of "lime-mortars" to throw it at the enemy ships. Limestone is a substitute for lime in many applications, which include agriculture, fluxing, and sulfur removal. Limestone, which contains less reactive material,
899-402: The homogeneous suspension of excess calcium hydroxide. This liquid has been known traditionally as milk of lime . Unprotected exposure to Ca(OH) 2 , as with any strong base , can cause skin burns, but it is not acutely toxic. Inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds — that is, a compound that
930-415: The layers. Calcium hydroxide is produced commercially by treating (slaking) quicklime with water: Alongside the production of quicklime from limestone by calcination , this is one of the oldest known chemical reactions; evidence of prehistoric production dates back to at least 7000 BCE. Calcium hydroxide is commonly used to prepare lime mortar . One significant application of calcium hydroxide
961-555: The material to above 825 °C (1,517 °F), a process called calcination or lime-burning , to liberate a molecule of carbon dioxide (CO 2 ), leaving quicklime behind. This is also one of the few chemical reactions known in prehistoric times. The quicklime is not stable and, when cooled, will spontaneously react with CO 2 from the air until, after enough time, it will be completely converted back to calcium carbonate unless slaked with water to set as lime plaster or lime mortar . Annual worldwide production of quicklime