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Calcium hydroxide-Wikipedia

Calcium hydroxide

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Calcium hydroxide

Calcium hydroxide

Mg(OH)2Xray.jpg

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

     checkY

3D model (

JSmol

)

  • Interactive image

  • Interactive image

ChEBI

  • CHEBI:31341

     checkY

ChemSpider

  • 14094

     checkY

ECHA InfoCard

100.013.762

Edit this at Wikidata

EC Number

  • 215-13

E number

E526

(acidity regulators, …)

Gmelin Reference

846915

KEGG

  • D01083

     checkY

PubChem

CID

  • 14777

RTECS number

  • EW2800000

UNII

  • PF5DZW74VN

     checkY

CompTox Dashboard

(EPA)

  • DTXSID7034410

    Edit this at Wikidata

InChI

  • InChI=1S/Ca.2H2O/h;2*1H2/q+2;;/p-2 checkY
    Key: AXCZMVOFGPJBDE-UHFFFAOYSA-L checkY
  • 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)

Solubility product

(Ksp)

5.5×10−6

Solubility

  • Soluble in

    glycerol

    and

    acids

    .

  • Insoluble in

    alcohol

    .

Basicity

(pKb)

1.37 (first OH), 2.43 (second OH)

[1]

[2]

Magnetic susceptibility

(χ)

−22.0·10−6 cm3/mol

Refractive index

(nD)

1.574
Structure

Crystal structure

Hexagonal,

hP3

[3]

Space group

P3m1 No. 164

Lattice constant

a = 0.35853 nm, c = 0.4895 nm
Thermochemistry

Std molar
entropy

(So298)

83 J·mol−1·K−1

[4]

Std enthalpy of
formation

fH298)

−987 kJ·mol−1

[4]

Hazards

Safety data sheet

See:

data page


[5]

GHS pictograms

GHS05: Corrosive

GHS07: Harmful

GHS Signal word

Danger

GHS hazard statements

H314, H318, H335, H402

GHS precautionary statements

P261, P280, P305+351+338

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.)

[6]

REL

(Recommended)

TWA 5 mg/m3

[6]

IDLH

(Immediate danger)

N.D.

[6]

Related compounds
Other

cations

Magnesium hydroxide

Strontium hydroxide

Barium hydroxide

Related

bases

Calcium oxide

Supplementary data page

Structure and
properties

Refractive index

(n),

Dielectric constant

r), etc.

Thermodynamic
data

Phase behaviour

solid–liquid–gas

Spectral data

UV

,

IR

,

NMR

,

MS

Except where otherwise noted, data are given for materials in their

standard state

(at 25 °C [77 °F], 100 kPa).

checkY 

verify

 (

what is

 checkY☒N ?)

Infobox references

Chemical compound

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

E number

E526.

Limewater

is the common name for a

saturated solution

of calcium hydroxide.

Properties[

edit

]

Calcium hydroxide is relatively insoluble in water, with a

solubility product Ksp

of 5.5×10−6. Its

acid dissociation constant

Ka is large enough that its solutions are basic according to the following reaction:

Ca(OH)2 → Ca2+ + 2 OH

At ambient temperature, calcium hydroxide (

portlandite

) dissolves in pure water to produce an alkaline solution with a pH of about 12.4. Calcium hydroxide solutions can cause chemical burns. At high pH value (see

common-ion effect

), its solubility drastically decreases. This behavior is relevant to cement pastes. Aqueous solutions of calcium hydroxide are called

limewater

and are medium-strength

bases

, which reacts with

acids

and can attack some

metals

such as

aluminium

(amphoteric hydroxide dissolving at high pH), while protecting other metals, such as

iron

and

steel

, from corrosion by

passivation

of their surface. Limewater turns milky in the presence of

carbon dioxide

due to formation of

calcium carbonate

, a process called

carbonatation

:

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:

[7]

Ca(OH)2 → CaO + H2O

Xem thêm: Chuyên đề Dấu của tam thức bậc hai và ứng dụng Đại số lớp 10 chi tiết

Structure, preparation, occurrence[

edit

]

SEM

image of fractured hardened cement paste, showing plates of calcium hydroxide and needles of

ettringite

(micron scale)

Calcium hydroxide adopts a

polymeric

structure, as do all metal hydroxides. The structure is identical to that of Mg(OH)2 (brucite structure); i.e., the

cadmium iodide

motif. Strong

hydrogen bonds

exist between the layers.

[8]

Calcium hydroxide is produced commercially by treating lime with water:

CaO + H2O → Ca(OH)2

In the laboratory it can be prepared by mixing

aqueous

solutions of

calcium chloride

and

sodium hydroxide

. The mineral form,

portlandite

, 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.

The positively charged ionized species CaOH+ has been detected in the atmosphere of

S-type stars

.

[9]

Retrograde solubility[

edit

]

The solubility of calcium hydroxide at 70 °C is about half of its value at 25 °C. The reason for this rather uncommon phenomenon is that the dissolution of calcium hydroxide in water is an exothermic process. Thus, according to

Le Chatelier’s principle

, a lowering of temperature favours the elimination of the heat liberated through the process of dissolution and increases the equilibrium constant of dissolution of Ca(OH)2, and so increase its solubility at low temperature. 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 retrograde solubility for the same reason because their dissolution reactions are exothermic.

Xem thêm: Phân dạng bài tập Anđehit Axit Cacboxylic-O2 Education

Uses[

edit

]

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.

It is also used in the preparation of ammonia gas (NH3), using the following reaction:

Ca(OH)2 + 2

NH4Cl

→ 2

NH3

+

CaCl2

+ 2 H2O

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.

[8]

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.

Food industry[

edit

]

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

    [10]

  • To clarify raw juice from

    sugarcane

    or

    sugar beets

    in the

    sugar industry

    , (see

    carbonatation

    )

  • To process water for alcoholic beverages and soft drinks
  • 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 digestive aid (called Choona, used in India in

    paan

    , a mixture of

    areca nuts

    , calcium hydroxide and a variety of seeds wrapped in betel leaves)

  • As a substitute for

    baking soda

    in making

    papadam

  • In the removal of carbon dioxide from controlled atmosphere produce storage rooms

Native American uses[

edit

]

Dry untreated maize (left), and treated maize (right) after boiling in water with calcium hydroxide (15 ml, or 1 tbsp, lime for 500 g of corn) for 15 minutes

In Spanish, calcium hydroxide is called cal. Maize cooked with cal (in a process of

nixtamalization

) becomes

hominy

(nixtamal), which significantly increases the bioavailability of

niacin

(vitamin B3), and is also considered tastier and easier to digest.

In chewing

coca leaves

, calcium hydroxide is usually chewed alongside to keep the

alkaloid

stimulants

chemically available for

absorption

by the body. Similarly, Native Americans traditionally chewed tobacco leaves with calcium hydroxide derived from burnt mollusc shells to enhance the effects. It has also been used by some indigenous American tribes as an ingredient in

yopo

, a psychedelic snuff prepared from the beans of some

Anadenanthera

species.

[11]

Asian uses[

edit

]

Calcium hydroxide is typically added to a bundle of

areca nut

and

betel

leaf called “

paan

” to keep the

alkaloid

stimulants

chemically available to enter the bloodstream via

sublingual

absorption.

It is used in making

naswar

(also known as nass or niswar), a type of dipping tobacco made from fresh tobacco leaves, calcium hydroxide (chuna or soon), and wood ash. It is consumed most in the

Pathan

diaspora,

Afghanistan

,

Pakistan

,

India

and

Bangladesh

. Villagers also use calcium hydroxide to

paint their mud houses

in Afghanistan, Pakistan and India.

Health risks[

edit

]

Unprotected exposure to Ca(OH)2 can cause severe skin irritation, chemical burns, blindness, lung damage or rashes.

[5]

Xem thêm: Tìm điều kiện của tham số m để đồ thị hàm số có 1, 2, 3 tiệm cận đứng. Dạng 2

See also[

edit

]

  • 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

References[

edit

]

  1. ^

    “Sortierte Liste: pKb-Werte, nach Ordnungszahl sortiert. – Das Periodensystem online”

    .

  2. ^

    ChemBuddy dissociation constants pKa and pKb

  3. ^

    Petch, H. E. (1961). “The hydrogen positions in portlandite, Ca(OH)2, as indicated by the electron distribution”. Acta Crystallographica. 14 (9): 950–957.

    doi

    :

    10.1107/S0365110X61002771

    .

  4. ^

    a

    b

    Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21.

    ISBN

     

    978-0-618-94690-7

    .

  5. ^

    a

    b

    “MSDS Calcium hydroxide”

    (PDF). Archived from

    the original

    (PDF) on 25 March 2012. Retrieved 21 June 2011.

  6. ^

    a

    b

    c

    NIOSH Pocket Guide to Chemical Hazards.

    “#0092”

    .

    National Institute for Occupational Safety and Health

    (NIOSH).

  7. ^

    Halstead, P. E.; Moore, A. E. (1957). “The Thermal Dissociation of Calcium Hydroxide”. Journal of the Chemical Society. 769: 3873.

    doi

    :

    10.1039/JR9570003873

    .

  8. ^

    a

    b

    Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann.

    ISBN

     

    0-7506-3365-4

    .

  9. ^

    Jørgensen, Uffe G. (1997),

    “Cool Star Models”

    , in van Dishoeck, Ewine F. (ed.), Molecules in Astrophysics: Probes and Processes, International Astronomical Union Symposia. Molecules in Astrophysics: Probes and Processes, 178, Springer Science & Business Media, p. 446,

    ISBN

     

    079234538X

    .

  10. ^

    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.

  11. ^

    de Smet, Peter A. G. M. (1985). “A multidisciplinary overview of intoxicating snuff rituals in the Western Hemisphere”. Journal of Ethnopharmacology. 3 (1): 3–49.

    doi

    :

    10.1016/0378-8741(85)90060-1

    .

    PMID

     

    3887041

    .

External links[

edit

]

  • National Organic Standards Board Technical Advisory Panel (4 April 2002).

    “NOSB TAP Review: Calcium Hydroxid”

    (PDF). Organic Materials Review Institute. Archived from

    the original

    (.PDF) on 31 October 2007. Retrieved 5 February 2008. Cite journal requires |journal= (

    help

    )

  • CDC – NIOSH Pocket Guide to Chemical Hazards – Calcium Hydroxide

  • MSDS Data Sheet

Retrieved from “

https://en.wikipedia.org/w/index.php?title=Calcium_hydroxide&oldid=1026987126

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