calcium hydroxide

 

Ca(OH)₂, colorless crystal or white powder. It is prepared by reacting calcium oxide (lime) with water, a process called slaking, and is also known as hydrated lime or slaked lime. When heated above 580°C it dehydrates, forming the oxide. Like the oxide, it has many uses, e.g., in liming soil, in sugar refining, and in preparing other compounds. It is a strong base and is widely used as an inexpensive alkali, often as a suspension in water (milk of lime); it is used in leather tanning to remove hair from hides. It is used in whitewash, mortar, and plaster. It is only slightly soluble in water, about 0.2 grams per 100 cubic centimeters, so its solutions are weakly basic. Limewater is a clear, saturated water solution of calcium hydroxide. It is used in medicine to treat acid burns and as an antacid. Because calcium hydroxide readily reacts with carbon dioxide, CO₂, to form calcium carbonate, a mixture of gases can be tested for the presence of CO₂ by shaking it with limewater in a clear container; if CO₂ is present, a cloudy calcium carbonate precipitate will form.

Calcium hydroxide
IUPAC name	Calcium hydroxide
Other names	Calcium(II) hydroxide, slaked lime, hydrated lime, Milk of Lime.
Identifiers
CAS number	1305-62-0
Properties
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	N/A
Solubility in water	0.185g/100 cm³ Ksp = 7.9 x 10−6
Basicity (pKb)	-2.37
Hazards
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 properties	n, εr, etc.
Thermodynamic data	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 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.

Uses

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
• 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]

Also, another name is Portlandite.

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]}

External links

• http://www.omri.org/CaOH_final.pdf
• MSDS Data Sheet.

References

1. ^ Temperature at which H₂O vapor pressure reaches 101 kPa, Halstead, Moore, J.Chem.Soc (1957) 3873

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