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Calcium hydroxide

Calcium hydroxide
IUPAC name Calcium hydroxide
Other names Calcium(II) hydroxide,
slaked lime,
hydrated lime,
Milk of Lime.
CAS number 1305-62-0
Molecular formula Ca(OH)2
Molar mass 74.093 g/mol
Appearance Soft white powder/Colourless liquid
Density 2.211 g/cm³, solid
Melting point

512°C (Decomposes).

Boiling point


Solubility in water 0.185g/100 cm³
Ksp = 7.9 x 10−6
Basicity (pKb) -2.37


MSDS External MSDS
EU classification Corrosive (C)
R-phrases R34, R36, R37, R38, R41.
S-phrases S22, S26, S39, S45.
Flash point Non-flammable.
Related Compounds
Other anions None listed.
Other cations None listed.
Related bases Calcium oxide.
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Calcium hydroxide, also known as slaked lime, is a chemical compound with the chemical formula Ca(OH)2. It is a colourless crystal or white powder, and is obtained when calcium oxide (called lime or quicklime) is mixed, or "slaked" with water. It can also be precipitated by mixing an aqueous solution of calcium chloride and an aqueous solution of sodium hydroxide. A traditional name for calcium hydroxide is slaked lime, or hydrated lime. The name of the natural mineral is portlandite.

If heated to 512°C,[1] calcium hydroxide decomposes into calcium oxide and water. A suspension of fine calcium hydroxide particles in water is called milk of lime. The solution is called lime water and is a medium strength base that reacts violently with acids and attacks many metals in presence of water. It turns milky if carbon dioxide is passed through, due to precipitation of calcium carbonate.


Because of its strong basic properties, calcium hydroxide has varied uses, such as

  • A flocculant, in water and sewage treatment and improvement of acid soils
  • An ingredient in whitewash, mortar, and plaster
  • An alkali used as a lye substitute in no-lye hair relaxers
  • A chemical depilatory agent found in Nair
  • An ingredient in baby formula milk
  • A chemical reagent
    • In the reef aquarium hobby for adding bio-available calcium in solution for calcium-using animals such as algae, snails, hard tube worms, and Corals (often referred to as Kalkwasser mix)
    • In the tanning industry for neutralization of extra acid
    • In the petroleum refining industry for the manufacture of additives to oils (salicatic, sulphatic, fenatic)
    • In the chemical industry for manufacture of calcium stearate
    • In the food industry for processing water (for alcoholic and soft drinks)
    • For clearing a brine of carbonates of calcium and magnesium in the manufacture of salt for food and pharmacopoeia
    • In Native American and Latin American cooking, calcium hydroxide is called "cal". Corn cooked with cal becomes nixtamal which significantly increases its nutrition value, and is also considered tastier and easier to digest.
    • In chewing Betel nut or coca leaves, calcium hydroxide is usually chewed alongside to keep the alkaloid stimulants chemically available for absorption by the body
  • A filler
    • In the petrochemical industry for manufacturing solid oil of various marks
    • In the manufacture of brake pads
    • In the manufacture of ebonite
    • For preparation of dry mixes for painting and decorating
    • In manufacturing mixes for pesticides
    • In manufacturing a drug called "Polikar" for fighting decay (due to fungus) of fruits and vegetables during storage
  • A dressing in paste form used for anti-microbial effect during a dental root canal procedure.[1]

Health risks

An overdose of Calcium hydroxide can have dangerous symptoms, including

  • Difficulty in breathing[citation needed]
  • Internal bleeding[citation needed]
  • Hypotension[citation needed]
  • Skeletal muscle paralysis, interference with actin-myosin system.
  • An increase in blood pH, which is damaging to the internal organs.[citation needed]


  1. ^ Temperature at which H2O vapor pressure reaches 101 kPa, Halstead, Moore, J.Chem.Soc (1957) 3873
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Calcium_hydroxide". A list of authors is available in Wikipedia.
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