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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, in the manufacture of 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.[1]

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 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.[2]

Borax was first discovered in dry lake beds in Tibet and was imported via the Silk Road to Arabia.[2] 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.[3][4]

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− 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.[5]

When borax is added to a flame, it produces a yellow green color.[6] 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.

EtymologyEdit

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".[7]

The word tincal /ˈtɪŋkəl/ "tinkle", or tincar /ˈtɪŋkər/ "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.[8]

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 the United States and many other countries) is refined by a process of recrystallization.[9]

File:Hauling Borax, Death Valley, 1904.jpg

Uses Edit

File:Borax.jpg

Household products Edit

Borax is used in various household laundry and cleaning products,[10] 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.[11] It is also an active ingredient in indoor and outdoor ant baits and killers and used for killing cockroaches.[12][13][14]

pH 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 dimethyl pimelimidate (DMP) based crosslinking reactions.

Co-complexing agentEdit

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 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)
Template:Magnesium2+ (aq) + Na2B4O7 (aq)Template:MagnesiumB4O7 (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.[15] Borax is often used as a flux for forge welding.

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.[16]

FlubberEdit

Main article: Flubber (material)

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.[17][18]

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.[19] 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 (Script error) or (Script error) 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.[1] 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.[2]

Other uses Edit

File:Boron mine pit.jpg

Toxicity Edit

Borax, sodium tetraborate decahydrate, according to one study, is not acutely toxic.[7] Its LD50 (median lethal dose) score is tested at 2.66 g/kg in rats,[8] 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. On pesticide information websites it is listed as a non-lethal compound and of no hazardous concerns.[9]

First registered in 1946 by the EPA as an insecticide with various restrictions, all restrictions were removed in February 1986 due to the low toxicity of Borax, as published in two EPA documents relating to boric acid and borax.[10][11]

EPA has determined that, because they are of low toxicity and occur naturally, boric acid and its sodium salts should be exempted from the requirement of a tolerance (maximum residue limit) for all raw agricultural commodities.[10]

Although it cited inconclusive data, a re-evaluation in 2006 by the EPA still found that "There were no signs of toxicity observed during the study and no evidence of cytotoxicity to the target organ."[12] In the reevaluation, a study of toxicity due to overexposure was checked and the findings were that "The residential handler inhalation risks due to boric acid and its sodium salts as active ingredients are not a risk concern and do not exceed the level of concern..." but that there could be some risk of irritation to children inhaling it if used as a powder for cleaning rugs.

Sodium tetraborate decahydrate has no known hazard issues.[13]

Conditions defined as "over-exposure" to borax dust can cause respiratory irritation, while no skin irritation is known to exist due to borax. 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."[14]

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".[15]

See also Edit

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References Edit

External links Edit

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