Limewater is the common name for a saturated aqueous solution of

calcium hydroxide 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 produced when quicklime (calcium oxide) is mixed or slaked with water. It has ma ...

. Calcium hydroxide, Ca(OH)₂, 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 is basic in nature with a pH of 12.4. 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), a milky solution results due to the homogeneous suspension of excess calcium hydroxide. This liquid has been known traditionally as milk of lime.

Chemistry

An experiment commonly used to demonstrate the interaction of CO₂ and Ca(OH)₂ is as follows. HCl + Ca(CO3)2 expt

Resultant carbon dioxide passed through limewater in the right tube, producing a milky solution due to

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

of the insoluble

suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspende ...

of calcium carbonate: : Ca(OH)₂ + CO₂ → CaCO₃ + H₂O If excess CO₂ is added: the following reaction takes place: : CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂ The milkiness disappears since calcium bicarbonate is water-soluble.

Applications

The above

chemical properties A chemical property is any of a material's properties that becomes evident during, or after, a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity.William L. Masterton, Cecile N. Hurley, ...

are commonly used for testing the presence of carbon dioxide in gaseous samples in school laboratories, and refining of

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or do ...

in a process called

carbonatation Carbonatation is a chemical reaction in which calcium hydroxide reacts with carbon dioxide and forms insoluble calcium carbonate: :Ca(OH)2CO2->CaCO3H_2O The process of forming a carbonate is sometimes referred to as "carbonation", although t ...

Industry

Waste gases from industries containing sulphur dioxide can be cleaned by bubbling through limewater, a process called

sulfation Sulfation is the chemical reaction that entails the addition of SO3 group. In principle, many sulfations would involve reactions of sulfur trioxide (SO3). In practice, most sulfations are effected less directly. Regardless of the mechanism, the ...

, in which the toxic sulphur dioxide is trapped as a precipitate: : Ca(OH)₂ + SO₂ → CaSO₃ + H₂O

Water treatment

Limewater is used in a process known as

lime softening Lime softening (also known as lime buttering, lime-soda treatment, or Clark's process) is a type of water treatment used for water softening, which uses the addition of limewater (calcium hydroxide) to remove hardness (deposits of calcium and magnes ...

to reduce water hardness. It is also used as a neutralizing agent in municipal waste water treatment.

Arts

In buon

fresco Fresco (plural ''frescos'' or ''frescoes'') is a technique of mural painting executed upon freshly laid ("wet") lime plaster. Water is used as the vehicle for the dry-powder pigment to merge with the plaster, and with the setting of the plast ...

painting, limewater is used as the colour solvent to apply on fresh plaster. Historically, it is known as the paint

whitewash Whitewash, or calcimine, kalsomine, calsomine, or lime paint is a type of paint made from slaked lime (calcium hydroxide, Ca(OH)2) or chalk calcium carbonate, (CaCO3), sometimes known as "whiting". Various other additives are sometimes used. ...

Dying Gaul (casting in Pushkin museum) 04 by shakko

Personal care and adornment

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 Diodorus Siculus, or Diodorus of Sicily ( grc-gre, Διόδωρος ; 1st century BC), was an ancient Greek historian. He is known for writing the monumental universal history '' Bibliotheca historica'', in forty books, fifteen of which ...

described the

Celts The Celts (, see pronunciation for different usages) or Celtic peoples () are. "CELTS location: Greater Europe time period: Second millennium B.C.E. to present ancestry: Celtic a collection of Indo-European peoples. "The Celts, an ancient ...

as follows: "Their aspect is terrifying... They are very tall in stature, with rippling muscles under clear white skin. Their hair 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...".

Food preparation

Limewater is used in the preparation of maize for

corn tortillas In North America, a corn tortilla or just tortilla (, ) is a type of thin, unleavened flatbread, made from hominy, that is the whole kernels of maize treated with alkali to improve their nutrition in a process called nixtamalization. A simple ...

and other culinary purposes using a process known as

nixtamalization Nixtamalization () is a process for the preparation of corn, or other grain, in which the grain is soaked and cooked in an alkaline solution, usually limewater (but sometimes aqueous alkali metal carbonates), washed, and then hulled. The ter ...

. Nixtamalization makes the

niacin Niacin, also known as nicotinic acid, is an organic compound and a form of vitamin B3, an essential human nutrient. It can be manufactured by plants and animals from the amino acid tryptophan. Niacin is obtained in the diet from a variet ...

nutritionally available and prevents

pellagra Pellagra is a disease caused by a lack of the vitamin niacin (vitamin B3). Symptoms include inflamed skin, diarrhea, dementia, and sores in the mouth. Areas of the skin exposed to either sunlight or friction are typically affected first. Over t ...

. Traditionally lime water was used in

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...

and

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...

to preserve

persimmon The persimmon is the edible fruit of a number of species of trees in the genus '' Diospyros''. The most widely cultivated of these is the Oriental persimmon, ''Diospyros kaki'' ''Diospyros'' is in the family Ebenaceae, and a number of non-per ...

and to remove

astringency An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissues. The word derives from the Latin ''adstringere'', which means "to bind fast". Calamine lotion, witch hazel, and yerba mansa, a Californian pla ...

Other uses

Limewater is widely used by marine aquarists as a primary supplement of

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

and

alkalinity Alkalinity (from ar, القلوي, al-qaly, lit=ashes of the saltwort) is the capacity of water to resist acidification. It should not be confused with basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength ...

for reef aquariums.

Coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...

s of order

Scleractinia Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a ...

build their

endoskeleton An endoskeleton (From Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is an internal support structure of an animal, composed of mineralized tissue. Overview An endoskeleton is a skeleton that is on the ...

s from

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

(a polymorph of calcium carbonate). When used for this purpose, limewater is usually referred to as ''Kalkwasser''. It is also used in tanning and making

parchment Parchment is a writing material made from specially prepared untanned skins of animals—primarily sheep, calves, and goats. It has been used as a writing medium for over two millennia. Vellum is a finer quality parchment made from the skins ...

. The lime is used as a dehairing agent based on its alkaline properties.''The Nature and Making of Parchment'' by Ronald Reed Calcium hydroxide is also applied in a leather process called liming.

References

{{DEFAULTSORT:Limewater Calcium compounds Hydroxides Chemical tests