Calcium hydroxide
Names | |
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IUPAC name
Calcium hydroxide
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Other names
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Identifiers | |
3D model (
JSmol ) |
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ChEBI | |
ChemSpider | |
ECHA InfoCard
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100.013.762 |
EC Number |
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E number | E526 (acidity regulators, ...) |
846915 | |
KEGG | |
PubChem CID
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RTECS number
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
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) |
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Solubility product (Ksp)
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5.02×10−6 [1] |
Solubility |
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Acidity (pKa) | 12.63 (first OH−), 11.57 (second OH−)[2][3] [clarification needed] |
−22.0·10−6 cm3/mol | |
Refractive index (nD)
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1.574 |
Structure | |
Hexagonal, hP3[4] | |
P3m1 No. 164 | |
a = 0.35853 nm, c = 0.4895 nm
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Thermochemistry | |
Std molar
entropy (S⦵298) |
83 J·mol−1·K−1[5] |
Std enthalpy of (ΔfH⦵298)formation |
−987 kJ·mol−1[5] |
Hazards | |
GHS labelling: | |
Danger | |
H314, H335, H402 | |
P261, P280, P305+P351+P338 | |
NFPA 704 (fire diamond) | |
Flash point | Non-flammable |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
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7340 mg/kg (oral, rat) 7300 mg/kg (mouse) |
NIOSH (US health exposure limits): | |
PEL (Permissible)
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TWA 15 mg/m3 (total) 5 mg/m3 (resp.)[7] |
REL (Recommended)
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TWA 5 mg/m3[7] |
IDLH (Immediate danger) |
N.D.[7] |
Safety data sheet (SDS) | [6] |
Related compounds | |
Other cations
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Magnesium hydroxide Strontium hydroxide Barium hydroxide |
Related bases
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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).
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Calcium hydroxide (traditionally called slaked lime) is an
Properties
Calcium hydroxide is poorly soluble in water, with a retrograde solubility increasing from 0.66 g/L at 100 °C to 1.89 g/L at 0 °C. With a
] its dissociation in water is large enough that its solutions are basic according to the following dissolution reaction:- Ca(OH)2 → Ca2+ + 2 OH−
At ambient temperature, calcium hydroxide (
- Ca(OH)2 + CO2 → CaCO3 + H2O
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:[8]
- Ca(OH)2 → CaO + H2O
Calcium hydroxide reacts with hydrogen chloride to first give calcium hydroxychloride and then calcium chloride.
Structure, preparation, occurrence
Calcium hydroxide adopts a
Calcium hydroxide is produced commercially by treating (slaking) lime with water:
- CaO + H2O → Ca(OH)2
In the laboratory it can be prepared by mixing
The positively charged ionized species CaOH+ has been detected in the atmosphere of S-type stars.[10]
Retrograde solubility
According to Hopkins and Wulff (1965),
The reason for this rather uncommon behavior is that the dissolution of calcium hydroxide in water involves an entropy decrease, due to the ordering of water molecules around the doubly charged calcium ion, This counter-intuitive temperature dependence of the solubility is referred to as "retrograde" or "inverse" solubility. The variably hydrated phases of calcium sulfate (gypsum, bassanite and anhydrite) also exhibit a slight retrograde solubility due to the presence of the calcium ion. However, other calcium salts like calcium chloride show an increase in solubility since the enthalpy change is larger and dominates the free energy change during dissolution. In all cases, the dissolution is exothermic.[citation needed]
Uses
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]
It is also used in the preparation of ammonia gas (NH3), using the following reaction:
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.[9] 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.[citation needed]
In
Calcium hydroxide is used in dentistry, primarily in the specialty of endodontics.
Food industry
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[20]
- 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)[21]
- 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[22]
Native American uses
In chewing
Asian uses
Calcium hydroxide is typically added to a bundle of
It is used in making
Health risks
Unprotected exposure to Ca(OH)2, as with any strong base, can cause severe skin irritation, chemical burns, blindness, lung damage or rashes.[6]
See also
- Baralyme (carbon dioxide absorbent)
- Cement
- Lime mortar
- Lime plaster
- Plaster
- Magnesium hydroxide (less alkaline due to a lower solubility product)
- Soda lime (carbon dioxide absorbent)
- Whitewash
- On Food and Cooking
References
- ^ ISBN 978-1138561632.
- ^ "Sortierte Liste: pKb-Werte, nach Ordnungszahl sortiert. – Das Periodensystem online".
- ^ ChemBuddy dissociation constants pKa and pKb
- .
- ^ ISBN 978-0-618-94690-7.
- ^ a b "MSDS Calcium hydroxide" (PDF). Archived from the original (PDF) on 25 March 2012. Retrieved 21 June 2011.
- ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0092". National Institute for Occupational Safety and Health (NIOSH).
- .
- ^ ISBN 0-7506-3365-4.
- ISBN 079234538X.
- ^ ISSN 0022-3654.
- ^ Berthelot, M. (1875). Dissolution des acides et des alcalis. [Dissolution of acids and alkalis]. In: Annales de Chimie et de Physique. Vol. 4, pp. 445–536.
- ^ Thomsen J. (1883). Thermochemische untersuchungen [Thermochemical studies]. Vol. III, Johann Ambrosius Barth Verlag, Leipzig.
- ISSN 0092-7325.
- ISSN 0002-7863.
- ISSN 0022-3654.
- ISSN 0016-7037.
- ISSN 0008-8846.
- ^ 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.
- ^ 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.
- ^ Borsook, Alec (6 August 2015). "Cooking with Alkali". Nordic Food Lab.
- ^ "Preparation of Mushroom Growing Substrates". North American Mycological Association. Retrieved 8 July 2021.
- PMID 3887041.
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.
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(help) - CDC – NIOSH Pocket Guide to Chemical Hazards – Calcium Hydroxide
- MSDS Data Sheet