Calcium hydroxide

Calcium hydroxide

Names
IUPAC name Calcium hydroxide
Other names Slaked lime Milk of lime Calcium(II) hydroxide Pickling lime Hydrated lime Portlandite Calcium hydrate Calcium dihydroxide
Identifiers
CAS Number	1305-62-0 Y
3D model ( JSmol )	Interactive image Interactive image
ChEBI	CHEBI:31341 Y
ChemSpider	14094 Y
ECHA InfoCard	100.013.762
EC Number	215-13
E number	E526 (acidity regulators, ...)
Gmelin Reference	846915
KEGG	D01083 Y
PubChem CID	14777
RTECS number	EW2800000
UNII	PF5DZW74VN Y
CompTox Dashboard (EPA)	DTXSID7034410
InChI InChI=1S/Ca.2H2O/h;2*1H2/q+2;;/p-2 Y Key: AXCZMVOFGPJBDE-UHFFFAOYSA-L Y InChI=1/Ca.2H2O/h;2*1H2/q+2;;/p-2 Key: AXCZMVOFGPJBDE-NUQVWONBAD
SMILES [Ca+2].[OH-].[OH-] [OH-].[OH-].[Ca+2]
Properties
Chemical formula	Ca(OH)2
Molar mass	74.093 g/mol
Appearance	White powder
Odor	Odorless
Density	2.211 g/cm3, solid
Melting point	580 °C (1,076 °F; 853 K) (loses water, decomposes)
Solubility in water	1.89 g/L (0 °C) 1.73 g/L (20 °C) 0.66 g/L (100 °C) (retrograde solubility, i.e., unusually decreasing with T)
Solubility product (Ksp)	5.02×10−6[1]
Solubility	Soluble in glycerol and acids. Insoluble in ethanol.[citation needed]
Acidity (pKa)	pKa1 = 12.63 pKa2 = 11.57[2][3]
Magnetic susceptibility (χ)	−22.0·10−6 cm3/mol
Refractive index (nD)	1.574
Structure
Crystal structure	Hexagonal, hP3[4]
Space group	P3m1 No. 164
Lattice constant	a = 0.35853 nm, c = 0.4895 nm
Thermochemistry
Std molar entropy (S⦵298)	83 J·mol−1·K−1[5]
Std enthalpy of formation (ΔfH⦵298)	−987 kJ·mol−1[5]
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H335, H402
Precautionary statements	P261, P280, P305+P351+P338
NFPA 704 (fire diamond)	3 0 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	7340 mg/kg (oral, rat) 7300 mg/kg (mouse)
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 15 mg/m3 (total) 5 mg/m3 (resp.)[7]
REL (Recommended)	TWA 5 mg/m3[7]
IDLH (Immediate danger)	N.D.[7]
Safety data sheet (SDS)	[6]
Related compounds
Other cations	Magnesium hydroxide Strontium hydroxide Barium hydroxide
Related bases	Calcium oxide
Supplementary data page
Calcium hydroxide (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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 with water. Annually, approximately 125 million tons of calcium hydroxide are produced worldwide.^[8]

Calcium hydroxide has many names including hydrated lime, caustic lime, builders' lime, slaked lime, cal, and pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as

Calcium hydroxide is moderately 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.

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:^[9]

Ca(OH)₂ → CaO + H₂O

When carbon dioxide is passed through limewater, the solution takes on a milky appearance due to precipitation of insoluble calcium carbonate:

Ca(OH)_2(aq) + CO_2(g) → CaCO_3(s) + H₂O_(l)

If excess CO₂ is added: the following reaction takes place:

CaCO_3(s) + H₂O_(l) + CO_2(g) → Ca(HCO₃)_2(aq)

The milkiness disappears since calcium bicarbonate is water-soluble.

Calcium hydroxide reacts with

Calcium hydroxide reacts with hydrochloric acid to give calcium hydroxychloride and then calcium chloride.

In a process called sulfation, sulphur dioxide reacts with limewater:

Ca(OH)_2(aq) + SO_2(g) → CaSO_3(s) + H₂O_(l)

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 is commonly used to prepare lime mortar.

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 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 is self-regulating and does not raise the pH too much.^{[citation needed]}

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 is the molten form of these chemicals from the recovery furnace.^[10]

In

Because of its low toxicity and the mildness of its basic properties, slaked lime is widely used in the food industry,

• In USDA certified food production in plants and livestock^[14]
• To clarify raw juice from sugarcane or sugar beets in the sugar industry (see carbonatation)
• To process water for alcoholic beverages and soft drinks
• To increase the rate of Maillard reactions (pretzels)^[15]
• Pickle cucumbers and other foods
• To make Chinese century eggs
• In maize preparation: removes the cellulose hull of maize kernels (see nixtamalization)
• To clear a brine of carbonates of calcium and magnesium in the manufacture of salt for food and pharmaceutical uses
• In fortifying (Ca supplement) fruit drinks, such as orange juice, and infant formula
• As a substitute for
  baking soda in making papadam
• In the removal of carbon dioxide from controlled atmosphere produce storage rooms
• In the preparation of mushroom growing substrates[16]

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.^{[citation needed}

]

Limewater is used in the preparation of maize for

corn tortillas and other culinary purposes using a process known as nixtamalization. Nixtamalization makes the niacin nutritionally available and prevents pellagra.^[17] Traditionally lime water was used in Taiwan and China to preserve persimmon and to remove astringency.^[18]

^: 623

In chewing

yopo, a psychedelic snuff prepared from the beans of some Anadenanthera species.^[19]

Asian uses

Calcium hydroxide, locally known as chuna, choona or soon, is typically added to a bundle of

sublingual

absorption.

Choona is a key ingredient in Petha, contributing to its characteristic crunchy and firm texture.

It is used in making

Pathan diaspora, Afghanistan, Pakistan, India and Bangladesh. Villagers also use calcium hydroxide to paint their mud houses

in Afghanistan, Pakistan and India.

Hobby uses

In buon fresco painting, limewater 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

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. The lime is used as a dehairing agent based on its alkaline properties.^[20]

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 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...".^[21][22]

Calcium hydroxide is also applied in a leather process called liming.

Interstellar medium

The ion CaOH⁺ has been detected in the atmosphere of S-type stars.^[23]

Limewater

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^[24]). "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 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 the homogeneous suspension of excess calcium hydroxide. This liquid has been known traditionally as milk of lime.

Health risks

Unprotected exposure to Ca(OH)₂, as with any strong base, can cause skin burns, but it is not acutely toxic.^[8]

See also

• Baralyme – Cabon dioxide scrubber absorbent mixture of calcium and barium hydroxides (carbon dioxide absorbent)
• Cement – Hydraulic binder used in the composition of mortar and concrete
• Lime mortar – Building material
• Lime plaster – Type of plaster composed of sand, water, and lime
• Plaster – Broad range of building and sculpture materials
• Magnesium hydroxide – Inorganic compound of formula Mg(OH)2 (less alkaline due to a lower solubility product)
• Soda lime – Chemical mixture for absorbing carbon dioxide
• Whitewash – Paint made from lime and chalk
• On Food and Cooking – Book by Harold McGee

References

1. ^
   ISBN 978-1138561632
   .
2. ^ "Sortierte Liste: pKb-Werte, nach Ordnungszahl sortiert. – Das Periodensystem online".
3. ^ ChemBuddy dissociation constants pK_a and pK_b
4. doi:10.1107/S0365110X61002771
   .
5. ^
   ISBN 978-0-618-94690-7
   .
6. ^ "MSDS Calcium hydroxide" (PDF). Archived from the original (PDF) on 25 March 2012. Retrieved 21 June 2011.
7. ^ ^{a b c} NIOSH Pocket Guide to Chemical Hazards. "#0092". National Institute for Occupational Safety and Health (NIOSH).
8. ^
   ISBN 978-3-527-30385-4
   .
9. doi:10.1039/JR9570003873
   .
10. ^
    ISBN 0-7506-3365-4
    .
11. ^ "History of limestone uses – timeline". Science Learning Hub – Pokapū Akoranga Pūtaiao. Curious Minds New Zealand. 1 October 2012. Retrieved 7 June 2024.
12. ^ European Union (13 May 2015). "COMMISSION IMPLEMENTING REGULATION (EU) 2015/762 of 12 May 2015 approving the basic substance calcium hydroxide in accordance with Regulation (EC) No 1107/2009 of the European Parliament and of the Council concerning the placing of plant protection products on the market, and amending the Annex to Commission Implementing Regulation (EU) No 540/2011". Retrieved 12 May 2022.
13. PMID 21535021
    .
14. ^ Pesticide Research Institute for the USDA National Organic Program (23 March 2015). "Hydrated Lime: Technical Evaluation Report" (PDF). Agriculture Marketing Services. Retrieved 17 July 2019.
15. ^ Borsook, Alec (6 August 2015). "Cooking with Alkali". Nordic Food Lab.
16. ^ "Preparation of Mushroom Growing Substrates". North American Mycological Association. Retrieved 8 July 2021.
17. ^ Wacher, Carmen (1 January 2003). "Nixtamalization, a Mesoamerican technology to process maize at small-scale with great potential for improving the nutritional quality of maize based foods". Food Based Approaches for a Healthy Nutrition in Africa. Archived from the original on 5 March 2018.
18. OCLC 58840243
    .
19. PMID 3887041
    .
20. ^ The Nature and Making of Parchment by Ronald Reed ^{[ISBN missing]}
21. ^ "Diodorus Siculus, Library of History | Exploring Celtic Civilizations".
22. ^ "Diodorus Siculus – Book V, Chapter 28". penelope.uchicago.edu. Retrieved 12 November 2017.
23. ISBN 079234538X
    .
24. ^ 'Solubility of Inorganic and Metalorganic Compounds – A Compilation of Solubility Data from the Periodical Literature', A. Seidell, W. F. Linke, Van Nostrand (Publisher), 1953 ^{[ISBN missing]}

External links

• National Lime Association. "Properties of typical commercial lime products. Solubility of calcium hydroxide in water" (PDF). lime.org. Retrieved 18 June 2021.
• National Organic Standards Board Technical Advisory Panel (4 April 2002). "NOSB TAP Review: Calcium Hydroxide" (PDF). Organic Materials Review Institute. Archived from the original (.PDF) on 31 October 2007. Retrieved 5 February 2008. {{cite journal}}: Cite journal requires |journal= (help)
• CDC – NIOSH Pocket Guide to Chemical Hazards – Calcium Hydroxide
• MSDS Data Sheet