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Borax

Borax
Borax crystals
Ball-and-stick model of the unit cell of borax decahydrate
Identifiers
CAS number  (decahydrate) YesY
ChemSpider  YesY
UNII  YesY
EC number
ChEMBL  N
ATC code S01
Jmol-3D images Image 1
Properties
Molecular formula Na2B4O7·10H2O or Na2[B4O5(OH)4]·8H2O
Molar mass 381.38 (decahydrate)
201.22 (anhydrate)
Appearance white solid
Density 1.73 g/cm3 (solid)
Melting point 743 °C (1,369 °F; 1,016 K) anhydrate[1]
Boiling point 1,575 °C (2,867 °F; 1,848 K)
Hazards
NFPA 704
0
1
0
Related compounds
Other anions Sodium aluminate; sodium gallate
Other cations Potassium tetraborate
Related compounds Boric acid, sodium perborate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N   YesY/N?)

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.[2]

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 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.[3]

Borax was first discovered in dry lake beds in Tibet and was imported via the Silk Road to Arabia.[3] 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 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.[4][5]

Contents

  • Chemistry 1
  • Etymology 2
  • Natural sources 3
  • Uses 4
    • Household products 4.1
    • pH buffer 4.2
    • Co-complexing agent 4.3
    • Water-softening agent 4.4
    • Flux 4.5
    • Small-scale gold mining 4.6
    • Flubber 4.7
    • Food additive 4.8
    • Other uses 4.9
  • Toxicity 5
  • See also 6
  • References 7
  • External links 8

Chemistry

The structure of the anion [B4O5(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. 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.[6] When borax is added to a flame, it produces a yellow green color.[7] Borax is not used for this purpose in fireworks due to the overwhelming yellow color of sodium. Boric acid is used to color methanol flames a transparent green.

Etymology

The English word borax is Latinized: the Middle English form was boras, from Old French boras, bourras. That may have been from medieval Latin baurach (another English spelling), borac(-/um/em), borax, or maybe directly from the Arabic, along with Spanish borrax (> borraj) and Italian borrace, in the 9th century. The Arabic was (is) بورق bauraq/būraq "natron", a word also used for borax. Traditional Arabic dictionaries say that it derives from the verb "to glisten", which is also written بورق bwrq, but it seems to actually derive from the Persian بوره būrah "borax".[8]

The word tincal "tinkle", or tincar "tinker", refers to crude borax, before it is purified, as mined from lake deposits in Tibet, Persia, and other parts of Asia. The word was adopted in the 17th century from Malay tingkal and from Urdu/Persian/Arabic تنکار tinkār/tankār; thus the two forms in English. These all appear to be related to the Sanskrit टांकण ṭānkaṇa.[9]

Natural sources

Borax "cottonball"

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 the United States and many other countries) is refined by a process of recrystallization.[10]

Traction steam engine hauling borax, Death Valley, California, 1904.

Uses

Borax-based washing detergent.

Household products

Borax is used in various household laundry and cleaning products,[11] 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.[12] It is also an active ingredient in indoor and outdoor ant baits and killers.

pH buffer

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 dimethyl pimelimidate (DMP) based crosslinking reactions.

Co-complexing agent

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.

Water-softening agent

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

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.[13]

Small-scale gold mining

Old steam tractor and borax wagons, Death Valley

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.[14]

Flubber

A rubbery polymer sometimes called Slime, Flubber, gluep or glurch (or erroneously called Silly Putty which is based on silicone polymers, instead), can be made by cross linking polyvinyl alcohol with borax. Making flubber from polyvinyl acetate based glues, such as Elmer's Glue, and borax is a common elementary-science demonstration.[15][16]

Food additive

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.[17] 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.[18] 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.[19]

Other uses

Rio Tinto Borax Mine Pit, Boron California

Toxicity

Borax, sodium tetraborate decahydrate, according to one study, is not acutely toxic.[24] Its LD50 (median lethal dose) score is tested at 2.66 g/kg in rats,[25] meaning that a significant dose of the chemical is needed to cause severe symptoms or death. The lethal dose is not necessarily the same for humans.

Sodium tetraborate decahydrate was once registered as an insecticide for a brief period, and the product was issued a "Danger" signal word by the EPA. Registration was allowed to lapse after the initial one year registration due to the fact the product could not be legally sold over the counter as an insecticide due to the dangers the product posed to the general public. Danger is the highest level signal word issued by the EPA.

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."[26]

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".[27]

See also

References

  1. ^ Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. p. 88.  
  2. ^ http://www.blacksmithinstitute.org/newsletter/march-april-filipino-gold-miner-reveals-borax-secret-pakistan-s-pollution-problem.html#topic1
  3. ^ a b "Borax ( Na2B4O7. 10H2O ) – Sodium Borate – Occurrence, Discovery and Applications". Amoz.com. 
  4. ^ "American Borax Production" Scientific American September 22, 1877
  5. ^ Hildebrand, G. H. (1982) "Borax Pioneer: Francis Marion Smith." San Diego: Howell-North Books. p. 267 ISBN 0-8310-7148-6
  6. ^ Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K. (2000), Vogel's Quantitative Chemical Analysis (6th ed.), New York: Prentice Hall,   p. 316.
  7. ^ Staff. "Creating Flame Colors". The Science Company. Retrieved November 30, 2008. 
  8. ^ "borax".  
  9. ^ "tincal".  
  10. ^ 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).  
  11. ^ Record in the Household Products Database of NLM
  12. ^ Hammond, C. R. (2004). The Elements, in Handbook of Chemistry and Physics 81st edition. CRC press.  
  13. ^ Dodd, J.G. (1966). "Soft soldering to tungsten wire". Am. J. Phys 34 (10): xvi.  
  14. ^ "The borax method". Borax replacing mercury in small-scale mining. The Geological Survey of Denmark and Greenland (GEUS). Retrieved 2008-08-02. 
  15. ^ Parratore, Phil. Wacky Science: A Cookbook for Elementary Teachers. Dubuque, IA: Kendall Hunt. p. 26.  
  16. ^ Step-By-Step Slime Instructions. Chemistry.about.com. Retrieved on 2012-02-17.
  17. ^ "Caviar glossary". The Caviar Guide a gourmet review of caviars & fish roe. Hanson Ltd, Geneva, Switzerland. Retrieved 2008-07-07. 
  18. ^ Chinese Ingredients: Borax Powder, Sep 11, 2005, Chow Hound, Home Cooking. Chowhound.chow.com. Retrieved on 2012-02-17.
  19. ^ Staff writer (2006). "Watch Out For The Food We Consume". Directorate of Consumer Protection, Jakarta, Indonesia. Retrieved 2009-02-10. 
  20. ^ Sarah Jenkinson and Nick Harrison Sheep's wool insulation in action! Centre for Alternative Technology (2000)
  21. ^ Borax at UC Berkeley
  22. ^ How To Color Fire. chemistry.about.com
  23. ^ Radweld safety data sheet Retrieved 19-02-2010
  24. ^ Borax – toxicity, ecological toxicity and regulatory information. Pesticideinfo.org. Retrieved on 2012-02-17.
  25. ^ Mountain Fresh Dial Bar Soap. (PDF) . Retrieved on 2012-02-17.
  26. ^ Borax – toxicity, ecological toxicity and regulatory information. Pesticideinfo.org. Retrieved on 2012-02-17.
  27. ^ 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.

External links

  • International Chemical Safety Card 0567
  • International Chemical Safety Card 1229 (fused borax)
  • National Pollutant Inventory – Boron and compounds
  • NIOSH Pocket Guide to Chemical Hazards
  • Sodium Borate in sefsc.noaa.gov
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