Borax
IUPAC name Sodium tetraborate decahydrate
Identifiers
CAS number	1303-96-4 (decahydrate) Y
ChemSpider	17339255 Y
UNII	91MBZ8H3QO Y
EC number	215-540-4
ChEMBL	CHEMBL1076681
Jmol-3D images	Image 1
SMILES [Na+].[Na+].[O-]B1OB2OB([O-])OB(O1)O2.O.O.O.O.O.O.O.O.O.O
InChI InChI=1S/B4O7.2Na.10H2O/c5-1-7-3-9-2(6)10-4(8-1)11-3;;;;;;;;;;;;/h;;;10*1H2/q-2;2*+1;;;;;;;;;; Y Key: CDMADVZSLOHIFP-UHFFFAOYSA-N Y InChI=1/B4O7.2Na.10H2O/c5-1-7-3-9-2(6)10-4(8-1)11-3;;;;;;;;;;;;/h;;;10*1H2/q-2;2*+1;;;;;;;;;; Key: CDMADVZSLOHIFP-UHFFFAOYAP
Properties
Molecular formula	Na2B4O7·10H2O or Na2[B4O5(OH)4]·8H2O
Molar mass	381.37 (decahydrate)
Appearance	white solid
Density	1.73 g/cm3 (solid)
Melting point	743 °C (anhydrous) [1]
Boiling point	1575 °C
Related compounds
Other anions	Sodium aluminate; sodium gallate
Other cations	Potassium tetraborate
Related compounds	Boric acid, sodium perborate
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Borax, also known as sodium borate, 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 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.

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:بورق is Arabic – the Arabic is said to be from the Persian burah, a word that may have meant potassium nitrate or another fluxing agent. 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 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.^[3][4]

Uses[link]

Borax-based washing detergent.

Household products[link]

Borax is used in various household laundry and cleaning products,^[5] including the "20 Mule Team Borax" laundry booster and "Boraxo" powdered hand soap. However, despite its name, "Borateem" laundry bleach no longer contains borax or other boron compounds. Borax is also present in some tooth bleaching formulas.^[6]

Buffer[link]

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[link]

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. Borate and a proprietary synthetic amino acid, Deselex (from Henkel) have been used to complex water "hardness" cations to make a non-precipitating water "softener". Borate alone does not have a high affinity for "hardness" cations, although it has been used for that purpose.

Flux[link]

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.^[7]

Small-scale mining[link]

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.^[8]

Putty[link]

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.^[9]

Food additive[link]

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.^[10] 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.^[11] 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.^[12]

Other uses[link]

• Ingredient in enamel glazes
• Component of glass, pottery, and ceramics
• Borax can be used as an additive in ceramic slips and glazes to improve fit on wet, greenware, and bisque.
• Fire retardant
• Anti-fungal compound for fiberglass and cellulose insulation
• Moth proofing 10% solution for wool^[13]
• Anti-fungal foot soak
• Precursor for sodium perborate monohydrate that is used in detergents, as well as for boric acid and other borates
• Tackifier ingredient in casein, starch and dextrin based adhesives
• Precursor for Boric acid, a tackifier ingredient in polyvinyl acetate, polyvinyl alcohol based adhesives
• Fluoride detoxification
• Treatment for thrush in horses' hooves
• Used to make indelible ink for dip pens by dissolving shellac into heated borax
• Curing agent for snake skins
• Curing agent for salmon eggs, for use in sport fishing for salmon
• Swimming pool buffering agent to control the pH
• Neutron absorber, used in nuclear reactors and spent fuel pools to control reactivity and to shut down a nuclear chain reaction
• As a micronutrient fertilizer to correct boron-deficient soils.^[14]
• To clean the brain cavity of a skull for mounting
• To color fires with a green tint^[15]
• Was traditionally used to coat dry-cured meats such as hams to protect them from becoming fly-blown during further storage.
• Is found in some commercial vitamin supplements
• For stopping car radiator and engine block leaks^[16]
• As an important component in Slime^[17]
• Is used by the modern Blacksmith in the process of Forge Welding. (Different from fabrication Gas or Electric style welding)

Natural sources[link]

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, 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.^[18]

Toxicity[link]

Borax, sodium tetraborate decahydrate, is not acutely toxic.^[19] Its LD₅₀ (median lethal dose) score is tested at 2.66 g/kg in rats:^[20] 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.^[21]

Boric acid solutions used as an eye wash or on abraded skin are known to be particularly toxic to infants, especially after repeated use, because of the slow elimination rate.^[22]

Borax was added to the Substance of Very High Concern (SVHC) candidate list on 16 December 2010. The SVHC candidlate 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".^[23]

Chemistry[link]

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 B(OH)₃ [or H₃BO₃] + 2 NaCl + 5 H₂O

The "decahydrate" is sufficiently stable to find use as a primary standard for acid base titrimetry.^[24]

When borax is added to a flame, it produces a yellow green color.^[25] 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[link]

References[link]

External links[link]

Wikimedia Commons has media related to: Borax

• 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