![Limewater](https://upload.wikimedia.org/wikipedia/commons/9/99/Limewater.jpg)
Limewater is the common name for a saturated aqueous solution of
calcium hydroxide. 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 CO
2 and Ca(OH)
2 is as follows.
![HCl + Ca(CO3)2 expt](https://upload.wikimedia.org/wikipedia/commons/8/85/HCl_%2B_Ca%28CO3%292_expt.png)
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 + CO
2 → CaCO
3 + H
2O
If excess CO
2 is added: the following reaction takes place:
: CaCO
3 + H
2O + CO
2 →
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 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 + SO
2 → CaSO
3 + H
2O
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 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.
...
.
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 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 ancien ...
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 nort ...
and
China 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.
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 t ...
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 ...
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
Tanning may refer to:
*Tanning (leather), treating animal skins to produce leather
*Sun tanning, using the sun to darken pale skin
**Indoor tanning, the use of artificial light in place of the sun
**Sunless tanning, application of a stain or dye t ...
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 o ...
. 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