Calcium hydroxide

Calcium hydroxide

Overview
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the chemical formula Ca
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

(OH
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

)2. It is a colourless crystal or white powder and is obtained when calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

 (called lime or quicklime) is mixed, or "slaked" with water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. It has many names including hydrated lime, builders lime, slack lime, cal, or pickling lime. It is of low toxicity and finds many applications, including for food.

When heated to 512 °C, the partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

 of water in equilibrium with calcium hydroxide reaches 101 kPa, which decomposes
Chemical decomposition
Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction...

 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.
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Encyclopedia
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the chemical formula Ca
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

(OH
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

)2. It is a colourless crystal or white powder and is obtained when calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

 (called lime or quicklime) is mixed, or "slaked" with water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. It has many names including hydrated lime, builders lime, slack lime, cal, or pickling lime. It is of low toxicity and finds many applications, including for food.

Properties


When heated to 512 °C, the partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

 of water in equilibrium with calcium hydroxide reaches 101 kPa, which decomposes
Chemical decomposition
Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction...

 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
Lime water
Limewater is the common name for saturated calcium hydroxide solution. It is sparsely soluble. Its chemical formula is Ca2. Since calcium hydroxide is only sparsely soluble, i.e. ca. 1.5 g per liter at 25 °C, there is no visible distinction to clear water. Attentive observers will notice a slightly...

 and is a medium strength base that reacts with acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

s and attacks many metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

s. Lime water turns milky in the presence of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 due to formation of calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

:
Ca(OH)2 + CO2 → CaCO3 + H2O


Calcium hydroxide crystallizes in the same motif as cadmium iodide
Cadmium iodide
Cadmium iodide, CdI2, is a chemical compound of cadmium and iodine. It is notable for its crystal structure, which is typical for compounds of the form MX2 with strong polarization effects.-Uses:...

. The layers are interconnected by hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...

s.

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
Calcium chloride
Calcium chloride, CaCl2, is a salt of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. Common applications include brine for refrigeration plants, ice and dust control on roads, and desiccation...

 and sodium hydroxide. The mineral form, portlandite
Portlandite
Portlandite is a rare oxide mineral, the naturally occurring form of calcium hydroxide . It is the calcium analogue of brucite .-Occurrence:...

, 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.

Uses


One significant application of calcium hydroxide is as a flocculant
Flocculation
Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually...

, in water and sewage treatment
Sewage treatment
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...

. 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
Kraft process
The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...

.

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
    Whitewash
    Whitewash, or calcimine, kalsomine, calsomine, or lime paint is a very low-cost type of paint made from slaked lime and chalk . Various other additives are also used...

    , mortar
    Lime mortar
    Lime mortar is a type of mortar composed of lime and an aggregate such as sand, mixed with water. It is one of the oldest known types of mortar, dating back to the 4th century BC and widely used in Ancient Rome and Greece, when it largely replaced the clay and gypsum mortars common to Ancient...

    , and plaster
    Plaster
    Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting,...

  • To fill the root canal for the first stage of endodontic therapy
    Endodontic therapy
    Endodontic therapy is a sequence of treatment for the pulp of a tooth which results in the elimination of infection and protection of the decontaminated tooth from future microbial invasion...

     (it is then replaced by rubber).
  • As an additive to sea water to reduce atmospheric CO2
    Carbon dioxide
    Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

     and mitigate the greenhouse effect
    Greenhouse effect
    The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...

    .
  • 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
    Alkali
    In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...

     used as a lye substitute in no-lye hair relaxer
    Relaxer
    A relaxer is a type of lotion or cream generally used by people with afro textured hair, which makes hair less curly and also easier to straighten by chemically "relaxing" the natural curls...

    s
  • A chemical depilatory
    Chemical depilatory
    A chemical depilatory is a cosmetic preparation used to remove the hair from the skin on the human body. Currently, a common active ingredient is calcium thioglycolate, which breaks down the disulphide bonds in keratin and weakens the hair so that it is easily scraped off where it emerges from the...

     agent found in most hair removal creams (for example Nair)
  • In Bordeaux mixture
    Bordeaux mixture
    Bordeaux mixture is a mixture of copper sulfate and slaked lime used as a fungicide in vineyards. It is used mainly to control garden, vineyard, nursery and farm infestations of fungi, primarily downy mildew which can result from infections of Plasmopara viticola. It was invented in the Bordeaux...

     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
    Stearic acid
    Stearic acid is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH316CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates...

    • In the petrochemical
      Petrochemical
      Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....

       industry for manufacturing solid oil of various marks
    • In the manufacture of brake pad
      Brake
      A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....

      s
    • In manufacturing the trademarked compound "Polikar", an antifungal
      Fungicide
      Fungicides are chemical compounds or biological organisms used to kill or inhibit fungi or fungal spores. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality and profit. Fungicides are used both in agriculture and to fight fungal infections in animals...

       and antimicrobial
      Antimicrobial
      An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes...

       preservative for vegetable
      Vegetable
      The noun vegetable usually means an edible plant or part of a plant other than a sweet fruit or seed. This typically means the leaf, stem, or root of a plant....

      s in storage
    • For preparation of dry mixes for paint
      Paint
      Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...

      ing and decorating
    • In manufacturing mixes for pesticide
      Pesticide
      Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

      s
    • In the manufacture of ebonite
      Ebonite
      Ebonite is a brand name for very hard rubber first obtained by Charles Goodyear by vulcanizing rubber for prolonged periods. It is about 30% to 40% sulfur. Its name comes from its intended use as an artificial substitute for ebony wood...

    • As a calcium
      Calcium
      Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

       supplement and pH/carbonate buffer (known as Kalkwasser
      Lime water
      Limewater is the common name for saturated calcium hydroxide solution. It is sparsely soluble. Its chemical formula is Ca2. Since calcium hydroxide is only sparsely soluble, i.e. ca. 1.5 g per liter at 25 °C, there is no visible distinction to clear water. Attentive observers will notice a slightly...

      ) 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.

Food industry


Because of its low toxicity and the mildness of its basic properties, it is widely used in the food industry
Food industry
The food production is a complex, global collective of diverse businesses that together supply much of the food energy consumed by the world population...

 and associated hobbies: Examples:
  • The separation of sugar from sugar cane or sugar beet
    Sugar beet
    Sugar beet, a cultivated plant of Beta vulgaris, is a plant whose tuber contains a high concentration of sucrose. It is grown commercially for sugar production. Sugar beets and other B...

    s in the sugar industry, see carbonatation
    Carbonatation
    Carbonatation is a chemical reaction in which calcium hydroxide reacts with carbon dioxide and forms insoluble calcium carbonate:The process of forming a carbonate is sometimes referred to as "carbonation", although this term usually refers to the process of dissolving carbon dioxide in...

  • For processing water for alcoholic beverages, soft drinks.
  • Used in the processing of Norwegian lutefisk
    Lutefisk
    Lutefisk or Lutfisk is a traditional dish of the Nordic countries and parts of the Midwest United States. It is made from aged stockfish or dried/salted whitefish and lye . It is gelatinous in texture, and has an extremely strong, pungent odor...

    . Dried cod
    Cod
    Cod is the common name for genus Gadus, belonging to the family Gadidae, and is also used in the common name for various other fishes. Cod is a popular food with a mild flavor, low fat content and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of...

     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
    Lefse
    Lefse is a traditional soft, Norwegian flatbread. Lefse is made out of potato, milk or cream and flour, and cooked on a griddle. Special tools are available for lefse baking, including long wooden turning sticks and special rolling pins with deep grooves.-Flavoring:There are many ways of...

    .
  • Home food preservation in the making of pickles
    Pickling
    Pickling, also known as brining or corning is the process of preserving food by anaerobic fermentation in brine to produce lactic acid, or marinating and storing it in an acid solution, usually vinegar . The resulting food is called a pickle. This procedure gives the food a salty or sour taste...

    .
  • Clearing a brine
    Brine
    Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...

     of carbonates of calcium and magnesium
    Magnesium
    Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

     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
    Infant formula
    Infant formula is a manufactured food designed and marketed for feeding to babies and infants under 12 months of age, usually prepared for bottle-feeding or cup-feeding from powder or liquid . The U.S...

  • 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
    Paan
    Paan, from the word pān is an Indian, Pakistani, Uttarvarshi and Southeast Asian tradition of chewing betel leaf with areca nut and slaked lime paste, and katha brown powder paste, with many regional and local variations...

    "
  • Use as alternative ingredient to baking soda (raising agent) in papadam. (South Indian flatbread)

Native American uses



In Native American
Indigenous peoples of the Americas
The indigenous peoples of the Americas are the pre-Columbian inhabitants of North and South America, their descendants and other ethnic groups who are identified with those peoples. Indigenous peoples are known in Canada as Aboriginal peoples, and in the United States as Native Americans...

 and Mesoamerican cooking, calcium hydroxide is called "cal". Corn cooked with cal becomes nixtamal
Nixtamalization
Nixtamalization typically refers to a process for the preparation of maize , or other grain, in which the grain is soaked and cooked in an alkaline solution, usually limewater, and hulled. The term can also refer to the removal via an alkali process of the pericarp from other grains such as sorghum...

 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
Alkaloid
Alkaloids are a group of naturally occurring chemical compounds that contain mostly basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Also some synthetic compounds of similar structure are attributed to alkaloids...

 stimulant
Stimulant
Stimulants are psychoactive drugs which induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced alertness, wakefulness, and locomotion, among others...

s 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
Yopo
"Ebene" redirects here. For the city in Mauritius, see Ebene City.Anadenanthera peregrina, also known as Yopo, Jopo, Cohoba, Mopo, Nopo, Parica or Calcium Tree, is a perennial tree of the Anadenanthera genus native to the Caribbean and South America. It grows up to 20 m tall, having a thorny bark...

, a psychedelic snuff prepared from the beans of some Anadenanthera
Anadenanthera
Anadenanthera is a genus of South American trees in the Legume family, Fabaceae. The genus contains two to four species, including A. colubrina and A. peregrina...

 species.

Afghan uses


Used in making naswar
Naswar
Naswar is a type of dipping tobacco, made from fresh tobacco leaves, calcium oxide , and wood ash. It is consumed most in the Pathan diaspora, Afghanistan, Pakistan, India and also in Sweden, Norway.-Usage:...

(also known as nass or niswar) is a type of dipping tobacco, made from fresh tobacco leaves, calcium hydroxide
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...

 (Chuna), and wood ash. calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

 plays an important role in making a naswar. It is consumed most in the Pathan
Pashtun people
Pashtuns or Pathans , also known as ethnic Afghans , are an Eastern Iranic ethnic group with populations primarily between the Hindu Kush mountains in Afghanistan and the Indus River in Pakistan...

 diaspora, Afghanistan
Afghanistan
Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...

, Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...

, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 and also in Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

, Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

. Villagers also use calcium hydroxide
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...

 as a paint on to their mud made houses all over Afghanistan and Pakistan.

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.

External links