Borax (from Persian burah[1][2]), also called sodium borate, or
sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of
boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.
Borax has a wide variety of uses. It is a component of many detergents, cosmetics, and enamel glazes. It is also used to make
buffer solutions in biochemistry, as a
fire retardant, as an anti-fungal compound for
fibreglass, as an insecticide, as a flux in metallurgy, and as a precursor for other boron
compounds.
The term borax is used for a number of closely related minerals or chemical compounds that differ in their
crystal water content, but usually refers to the decahydrate. Commercially sold
borax is usually partially dehydrated.
Name
The origin of the name is traceable to the Medieval Latin borax, which comes from the Arabic buraq, which comes
from either the Persian burah [1] or the Middle Persian burak [2].
Uses
Buffer
Sodium borate is used in biochemical and chemical
laboratories to make buffer solutions, e.g. for gel electrophoresis of DNA. It has a lower conductivity, produces sharper bands, and can be run at higher speeds than can gels made from
TBE buffer or TAE buffer (5 - 35 V/cm as compared to 5 - 10 V/cm). At a given voltage, the heat generation and thus the gel temperature is much
lower than with TBE or TAE buffers, therefore the voltage can be increased to speed up electrophoresis so that a gel run takes
only a fraction of the usual time. Downstream applications, such as isolation of DNA from a gel slice or southern blot analysis, work as expected with sodium borate gels. Borate buffers (usually at pH 8) are
also used as preferential equilibration solution in DMP-based crosslinking reactions.
Lithium borate is similar to sodium borate and has all of its advantages, but permits
use of even higher voltages due to the lower conductivity of lithium ions as compared to sodium ions.[3] However, lithium borate is much more expensive.
Flux
A mixture of borax and ammonium chloride is used as a flux when welding iron and steel. It lowers the melting point of the unwanted
iron oxide (scale), allowing it to run off. Borax is also used mixed with water as a
flux when soldering jewelry metals such as gold or silver. It allows the molten
solder to flow evenly over the joint in question. Borax is also a good flux for 'pre-tinning'
tungsten with zinc - making the tungsten soft-solderable.[4]
Food additive
Borax is used as a food additive in some countries with the E number E285, but is banned in the United States. Its use is similar to salt, and it appears in French
and Iranian caviar.
Other uses
Natural sources
Borax occurs naturally in evaporite deposits produced by the repeated evaporation of
seasonal lakes (see playa). The most commercially important deposits are found in Turkey and near Boron, California and other locations in the
Southwestern United States, the Atacama
desert in Chile, and in Tibet. Borax can also be produced
synthetically from other boron compounds.
Toxicity
Boric acid, sodium borate, and sodium perborate are estimated to have a lethal dose (LD50) from 0.1 to 0.5 g/kg in humans [verification needed][5]. These substances are toxic to all cells, and have a slow excretion rate through
the kidneys. Kidney toxicity is the greatest, with liver fatty degeneration, cerebral edema, and gastroenteritis. Boric acid
solutions used as an eye wash or on abraded skin are known to be especially toxic to infants, especially after repeated use
because of its slow elimination rate.[6]
Chemistry
The structure of the anion [B
4O
5(OH)
4]
2− in borax
The term borax is often used for a number of closely related minerals or chemical compounds that differ in their
crystal water content:
- Anhydrous borax (Na2B4O7)
- Borax pentahydrate (Na2B4O7·5H2O)
- Borax decahydrate (Na2B4O7·10H2O)
Borax is generally described as Na2B4O7·10H2O. However, it is better formulated as
Na2[B4O5(OH)4]·8H2O, since borax contains the
[B4O5(OH)4]2− ion. In this structure, there are two four-coordinate boron atoms (two
BO4 tetrahedra) and two three-coordinate boron atoms (two BO3 triangles).
Borax is also easily converted to boric acid and other borates, which have many applications. If left exposed to dry air, it slowly loses its water of hydration and becomes the white and chalky mineral tincalconite (Na2B4O7·5H2O).
When borax is burned, it produces a bright orange-colored flame. Because of this, it is sometimes used for homemade
pyrotechnics.
See also
References
|
The references in this article would be clearer with a different or consistent style of citation, footnoting, or external
linking. |
- ^ "borax." Webster's Third New International Dictionary, Unabridged.
Merriam-Webster, 2002. http://unabridged.merriam-webster.com
- ^ "borax", OED
- ^ doi:10.1016/j.ab.2004.05.054 Analytical
Biochemistry 2004; 333: 1-13
- ^ doi:10.1119/1.1972398 Am. J. Phys. 34, xvi (1966)
- ^ Handbook of Poisoning, Robert H. Dreisback, eighth edition,
p.314
- ^ Goodman and Gillman's: The Pharmacological Basis of Therapeutics, 6th
edition, chapter on Antiseptics and Disinfectants, page 971
External links
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