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Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. Powdered borax is white, 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 fiberglass, as a flux in metallurgy, neutron-capture shields for radioactive sources, a texturing agent in cooking, and as a precursor for other boron compounds.

In artisanal gold mining, the borax method is sometimes used as a substitute for toxic mercury in the gold extraction process. Borax was reportedly used by gold miners in parts of the Philippines in the 1900s.

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.

The word borax is from Arabic būraq (بورق), meaning "white"; which is indeed from Middle Persian bwrk, which might have meant potassium nitrate or another fluxing agent, now known as būrah (بوره). Another name for borax is tincal, from Sanskrit.[1]

Borax was first discovered in dry lake beds in Tibet and was imported via the Silk Road to Arabia.[1] Borax first came into common use in the late 19th century when Francis Marion Smith's Pacific Coast Borax Company began to market and popularize a large variety of applications under the famous 20 Mule Team Borax trademark, named for the method by which borax was originally hauled out of the California and Nevada deserts in large enough quantities to make it cheap and commonly available.[2][3]

150 pounds of borax per ton of sand

Uses Edit

File:Borax.jpg

Household products Edit

Borax is used in various household laundry and cleaning products,[4] including the "20 Mule Team Borax" laundry booster and "Boraxo" powdered hand soap. Despite its name, "Borateem" laundry bleach no longer contains borax or other boron compounds. Borax is also present in some tooth bleaching formulas.[5] It is also an active ingredient in indoor and outdoor ant baits and killers.

Buffer Edit

Sodium borate is used in biochemical and chemical laboratories to make buffers, e.g. for gel electrophoresis of DNA, such as TBE or the newer SB buffer or BBS (borate buffered saline) in coating procedures. Borate buffers (usually at pH 8) are also used as preferential equilibration solution in DMP-based crosslinking reactions.

Co-complexing Edit

Borax as a source of borate has been used to take advantage of the co-complexing ability of borate with other agents in water to form complex ions with various substances. Borate and a suitable polymer bed are used to chromatograph non-glycosylated hemoglobin differentially from glycosylated hemoglobin (chiefly HbA1c), which is an indicator of long term hyperglycemia in diabetes mellitus.

As a water-softening agentEdit

Borax alone does not have a high affinity for the hardness cations, although it has been used for that purpose. Its chemical equation for water-softening is given below:

Ca2+ (aq) + Na2B4O7 (aq)CaB4O7 (s)↓ + 2 Na+ (aq)
Mg2+ (aq) + Na2B4O7 (aq)MgB4O7 (s)↓ + 2 Na+ (aq)

The sodium ions introduced do not make water ‘hard’. This method is suitable for removing both temporary and permanent types of hardness.

Flux Edit

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.[6]

Small-scale gold mining Edit

File:Borax wagons.jpg

Borax is replacing mercury as the preferred method for extracting gold in small-scale mining facilities. The method is called the borax method and is used in the Philippines.[7] Watch video of the borax method here.

PuttyEdit

A rubbery polymer sometimes called flubber, gluep or glurch can be made by cross linking polyvinyl acetate with a borax. Making flubber from polyvinyl acetate based glues, such as Elmer's Glue, and borax is a common elementary education experiment.[8]

Food additive Edit

Borax, given the E number E285, is used as a food additive in some countries, but is banned in the US. As a consequence, certain foods, such as caviar, produced for sale in the US contain higher levels of salt to assist preservation.[9] Its use as a cooking ingredient is to add a firm rubbery texture to the food, or as a preservative. In oriental cooking it is mostly used for its texturing properties. In Asia, Borax (Chinese: 硼砂; pinyin: péng shā) or (Chinese: 月石; pinyin: yuè shí) was found to have been added to some Chinese foods like hand-pulled noodles lamian and some rice noodles like Shahe fen, Kway Teow, and Chee Cheong Fun recipes.[10] In Indonesia it is a common, but forbidden, additive to such foods as noodles, bakso (meatballs), and steamed rice. The country's Directorate of Consumer Protection warns of the risk of liver cancer with high consumption over a period of 5–10 years.[11]

Other uses Edit

Natural sources Edit

File:Borax ball.jpg

Borax occurs naturally in evaporite deposits produced by the repeated evaporation of seasonal lakes. The most commercially important deposits are found in Turkey; Boron, California; and Searles Lake, California. Also, borax has been found at many other locations in the Southwestern United States, the Atacama desert in Chile, newly-discovered deposits in Bolivia, and in Tibet and Romania. Borax can also be produced synthetically from other boron compounds. Naturally occurring Borax, (known by the trade name Rasorite – 46 in USA and many other countries) is refined by a process of re-crystallization.[17]

Toxicity Edit

Borax, sodium tetraborate decahydrate, is not acutely toxic.[18] Its LD50 (median lethal dose) score is tested at 2.66 g/kg in rats:[19] a significant dose of the chemical is needed to cause severe symptoms or death. The lethal dose is not necessarily the same for humans.

Sufficient exposure to borax dust can cause respiratory and skin irritation. Ingestion may cause gastrointestinal distress including nausea, persistent vomiting, abdominal pain, and diarrhea. Effects on the vascular system and brain include headaches and lethargy, but are less frequent. "In severe poisonings, a beefy red skin rash affecting palms, soles, buttocks and scrotum has been described. With severe poisoning, erythematous and exfoliative rash, unconsciousness, respiratory depression, and renal failure."[20]

Borax was added to the Substance of Very High Concern (SVHC) candidate list on 16 December 2010. The SVHC candidate list is part of the EU Regulations on the Registration, Evaluation, Authorisation and Restriction of Chemicals 2006 (REACH), and the addition was based on the revised classification of Borax as toxic for reproduction category 1B under the CLP Regulations. Substances and mixtures imported into the EU which contain Borax are now required to be labelled with the warnings "May damage fertility" and "May damage the unborn child".[21]

Chemistry Edit

File:Tetraborate-xtal-3D-balls.png

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−</sub> 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. Its reaction with hydrochloric acid to form boric acid is:

Na2B4O7·10H2O + 2 HCl → 4 H3BO3 + 2 NaCl + 5 H2O

The "decahydrate" is sufficiently stable to find use as a primary standard for acid base titrimetry.[22]

When borax is added to a flame, it produces a yellow green color.[23] This property has been tried in amateur fireworks,[citation needed] but borax in this use is not popular because its waters of hydration inhibit combustion of compositions and make it an inferior source of the boron that is responsible for most of the green color, and that is overwhelmed by the yellow contributed to the flame by sodium.

However, commercially available borax can be mixed with flammables such as methanol to give the characteristic green flame of boron when ignited, which then slowly gives way to the characteristic yellow-orange flame of the sodium.

See also Edit

References Edit

  1. 1.0 1.1 Borax ( Na2B4O7. 10H2O ) – Sodium Borate – Occurrence, Discovery and Applications. Amoz.com.
  2. "American Borax Production" Scientific American September 22, 1877
  3. Hildebrand, G. H. (1982) "Borax Pioneer: Francis Marion Smith." San Diego: Howell-North Books. p. 267 ISBN 0-8310-7148-6
  4. Record in the Household Products Database of NLM
  5. Hammond, C. R. (2004). The Elements, in Handbook of Chemistry and Physics 81st edition. CRC press. ISBN 0-8493-0485-7. 
  6. Dodd, J.G. (1966). "Soft soldering to tungsten wire". Am. J. Phys 34 (10): xvi. doi:10.1119/1.1972398. 
  7. The borax method. Borax replacing mercury in small-scale mining. The Geological Survey of Denmark and Greenland (GEUS). Retrieved on 2008-08-02.
  8. Parratore, Phil. Wacky Science: A Cookbook for Elementary Teachers. Dubuque, IA: Kendall Hunt. p. 26. ISBN 0-7872-2741-2. 
  9. Caviar glossary. The Caviar Guide a gourmet review of caviars & fish roe. Hanson Ltd, Geneva, Switzerland. Retrieved on 2008-07-07.
  10. Chinese Ingredients: Borax Powder, Sep 11, 2005, Chow Hound, Home Cooking. Chowhound.chow.com. Retrieved on 2012-02-17.
  11. Staff writer (2006). Watch Out For The Food We Consume. Directorate of Consumer Protection, Jakarta, Indonesia. Retrieved on 2009-02-10.
  12. Sarah Jenkinson and Nick Harrison Sheep's wool insulation in action! Centre for Alternative Technology (2000)
  13. Borax at UC Berkeley
  14. How To Color Fire. chemistry.about.com
  15. Radweld safety data sheet Retrieved 19-02-2010
  16. Step-By-Step Slime Instructions. Chemistry.about.com. Retrieved on 2012-02-17.
  17. Wizniak, Jaime (July 2005). "Borax, Boric Acid, and Boron – From exotic to commodity". Indian Journal of Chemical Technology (New Delhi: Council of Scientific and Industrial Research) 12 (4). ISSN 0975-0991. http://nopr.niscair.res.in/bitstream/123456789/8663/1/IJCT%2012(4)%20488-500.pdf. 
  18. Borax – toxicity, ecological toxicity and regulatory information. Pesticideinfo.org. Retrieved on 2012-02-17.
  19. Mountain Fresh Dial Bar Soap. (PDF) . Retrieved on 2012-02-17.
  20. Borax – toxicity, ecological toxicity and regulatory information. Pesticideinfo.org. Retrieved on 2012-02-17.
  21. Member state committee draft support document for identification of disodium tetraborate, anhydrous as a substance of very high concern because of its CMR properties. Adopted on 9 June 2010. Echa.europa.eu. Retrieved on 2012-02-17.
  22. Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K. (2000), Vogel's Quantitative Chemical Analysis (6th ed.), New York: Prentice Hall, ISBN 0-582-22628-7  p. 316.
  23. Staff. Creating Flame Colors. The Science Company. Retrieved on November 30, 2008.

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