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Element Index
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Seaborgium
Selenium
Silicon
Sodium
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Sulfur
Chemical's truth
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Sodium hydroxide
(caustic soda, soda lye, sodium hydrate)
CAS no: 1310-73-2 Formula: NaOH Molecular weight: 39.997
Physical Data
Appearance: White orthorhombic hygroscopic crystals, often appear as pellets
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Melting point: 323°C
Boiling point: 1388°C
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Density: 2.13 g/cm3
Solubility: 100 g/100 g H2O
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Thermodynamic Data
Enthalpy of formation: -
Gibbs energy of formation: -
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Entropy: -
Heat capacity: -
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Production and preparation
Sodium hydroxide can be prepared by reacting calcium hydroxide with sodium carbonate (Gossage Process); from sodium chloride by electrolysis; or sodium metal and water vapour at low temperature.
In the laboratory, sodium hydroxide may be purified from sodium salts by dissolving it in alcohol. The salt itself does not dissolve but any organic contaminant can be removed by evaporating off the alcohol.
Ordinary solid sodium hydroxide always contains sodium carbonate (see below). However, if it is dissolve in an equal valume of carbon dioxide-free water, the carbonate remains insoluble and can be filtered off
through glass wool.
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Behavior and Chemical Properties
Sodium hydroxide rapidly adsorbs water and react with carbon dioxide in air to give sodium carbonate, usually in the form of a crust on the hydroxide surface:
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It is very soluble in water, soluble in methonal, ethanol and glycerol. On dissolving in water, it is a strong alkaline solution with a pH ~ 14 even with a 5 % solution. Concentrated solution also slowly dissolves glass to give
sodium silicate and therefore the solution must not be kept in glass bottle unless lined with parafix wax.
The strong alkaline solution form hydroxide precipitates of many metal ions in solutions. Some of these hydroxides, such as that of aluminium and zinc, are soluble when excess sodium hydroxide is
added to give soluble sodium salts.
Ammonia gas is evolved when heated with ammonium salts. This can be used as a test for ammonium salts.
Sodium hydroxide dissolves white phosphorus to give phosphine and sodium hypophosphite.
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History and Uses
Sodium hydroxide has wide range of uses in chemical and manufacturing industries, making a variety of sodium salts. It is commercially prepared in the form of pallets, sticks or chips.
It is used to neutralised acids and pH control. For example, in petroleum
refining to remove sulfuric acid and organic acids.
It is used to treat cellulose in making viscose rayon and cellophane and in reclaiming rubber by dissolving out the fabric. In textiles, sodium hydroxide is used in mercerization processes to increase strength and affinity for dyes. The process
was discovered in 1844 by John Mercer, an English calico printer. He received a patent for it in 1850.
Sodium hydroxide is also important in making soap, detergents by hydrolyzing fats, and in stabilizing sodium hypochlorite, an important disinfectant.
It is also used in paper making and glass manufacturing.
It mixes with calcium hydroxide to give soda lime, a grayish white substance, use medically to absorb carbon dioxide or other toxic gases. Soda lime
is also used in the laboratory as a drying agent.
Pure sodium hydroxide is used in the laboratory for volumetric analysis. The solution, however, must be protected from air to avoid the formation of sodium carbonate.
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Hazard, Storage and Handling
Keep in air-tight approved plastic container and away from incompatible substances such as metals, acids, ammonium compounds,
cyanides, nitro compounds and combustible organic chemicals. Solution can become very hot, especially if small amount of water is used to dissolve the chemical. Concentrated solution can attack glass.
Sodium hydroxide is very corrosive. It can cause severe burns leading to permanent blindness and scars and even death. The LD50 for mouse is 40 mg/kg. Breathing the dust can irritate throat, lungs and cause coughing. Higher dose
can result pulmonary edema which may cause death.
Upon eye and skin contact, splash immediately with plenty of water and seek emergency medical attention. If swallowed, given large amount of water if the victim is concious. Do not induce vomit. Seek immediate medical attention.
Safety googles and protective gloves (neoprene or PVC) and clothing must be worn when handling the chemicals.
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(Last update: March 2006) |
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