Difference between revisions of "Borate" - New World Encyclopedia
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== Natural occurrence == | == Natural occurrence == | ||
| − | [[Boron, California|Boron]], [[California]], contains large borax deposits that are extensively mined for borate. The [[Atacama Desert]] in [[Chile]] also contains mineable borate concentrations. [[Gerry, New York|Gerry]], [[New York]], has been described by [[Agapito Associates Inc.]] as a "very nice place" to mine for borate. Critics, however, are concerned about how mining might potentially damage the surrounding area. | + | Some of the naturally occurring borate minerals are [[borax]], [[colemanite]], and [[ulexite]]. Borax can be found in [[evaporite]] deposits produced by the repeated evaporation of seasonal lakes. From a commercial standpoint, the most important deposits of borax are located in [[Turkey]], near [[Boron, California]] and other parts of the southwestern [[United States]], the [[Atacama desert]] in [[Chile]], and [[Tibet]]. |
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| + | * [[Boron, California|Boron]], [[California]], contains large borax deposits that are extensively mined for borate. The [[Atacama Desert]] in [[Chile]] also contains mineable borate concentrations. [[Gerry, New York|Gerry]], [[New York]], has been described by [[Agapito Associates Inc.]] as a "very nice place" to mine for borate. Critics, however, are concerned about how mining might potentially damage the surrounding area. | ||
== Chemical structure and properties == | == Chemical structure and properties == | ||
Revision as of 02:13, 12 January 2009
Borates are chemical compounds containing boron oxoanions. The simplest borate ion is BO33−, although many others are known.[1] The anion BO33− can be found in salts with metallic elements. Many borates are readily hydrated to include structural hydroxide groups, and they should formally be considered hydroxoborates.
In nature, boron is commonly found as a borate mineral. It is also found combined with silicate to form complex borosilicate minerals such as the tourmalines.
Natural occurrence
Some of the naturally occurring borate minerals are borax, colemanite, and ulexite. Borax can be found in evaporite deposits produced by the repeated evaporation of seasonal lakes. From a commercial standpoint, the most important deposits of borax are located in Turkey, near Boron, California and other parts of the southwestern United States, the Atacama desert in Chile, and Tibet.
- Boron, California, contains large borax deposits that are extensively mined for borate. The Atacama Desert in Chile also contains mineable borate concentrations. Gerry, New York, has been described by Agapito Associates Inc. as a "very nice place" to mine for borate. Critics, however, are concerned about how mining might potentially damage the surrounding area.
Chemical structure and properties
As noted above, many borates are known. The simplest borate contains the ion BO33−, in which the atoms are arranged in a trigonal planar arrangement. In this and other borate ions, the oxidation state of boron is +3.
- Some borates are good buffers, balancing acidity and alkalinity.
- The inclusion of borates in glass increases its strength and resistance to heat and chemicals.
- Upon interacting with surfaces of materials containing iron, borates form a coating that prevents corrosion.
Aqueous chemistry
In aqueous solution, borate exists in many forms. In acidic and near-neutral conditions, it is boric acid, commonly written as H3BO3 but more correctly B(OH)3. The pKa of boric acid is 9.14 at 25C. Boric acid does not dissociate in aqueous solution, but is acidic due to its interaction with water molecules, forming tetrahydroxyborate:
- B(OH)3 + H2O ⇌ B(OH)4− + H+
- Ka = 5.8x10−10 mol/l; pKa = 9.24.
- B(OH)3 + H2O ⇌ B(OH)4− + H+
Polymeric anions containing structural OH units (polyhydroxoborates) are formed at pH 7–10 if the boron concentration is higher than about 0.025 mol/L. The best known of these is the ion, found in the mineral borax:
- 4B(OH)4− + 2H+ ⇌ B4O5(OH)4 2− + 7H2O
Even though boric acid adds hydroxide to form B(OH)4−, you may find for pKa values and other calculations, the fictitious ions are easier to use. Thus for a typical polyprotic acid, the deprotonation series dihydrogen borate [H2BO3−;], hydrogen borate [HBO32−] and borate [BO33−] may be written as pH increases.
Polymeric ions
A number of polymeric borate ions are known in anhydrous compounds, which are made by reacting B(OH)3 or B2O3 with metal oxides.[1] Examples include:
- diborate B2O54− e.g. in Mg2B2O5 (suanite)
- triborate B3O75 in CaAlB3O7 (johachidolite)
- tetraborate B4O96− in e.g. Li6B4O9
- metaborates containing the linear [BO2−]n with three coordinate boron e.g. in LiBO2, CaB2O4
- metaborates containing 3 and four coordinate boron, often these are high pressure modifications.
Common borate salts
Common borate salts include sodium metaborate, NaBO2, and sodium tetraborate, Na2B4O7, which is usually encountered as borax the so-called decahydrate, and actually contains the hydroxoborate ion, B4O5(OH)42− and is formulated Na2[B4O5(OH)4]·8H2O.
Borate esters
Borate esters are organic compounds of the type B(OR)3 where R is an organic residue (for example alkyl or aryl). Borate esters include trimethyl borate, B(OCH3)3, which is used as a precursor to boronic esters for Suzuki couplings.
Effects on living organisms
Boron is an essential micronutrient for plant growth, and plants obtain it from borates in the soil. People regularly consume borates that may be present in water and plant foods, but it is unclear whether boron is an essential ingredient for the human diet. In any case, borates are nontoxic for humans and many animals. By contrast, borates inhibit the growth of bacteria and fungi, and they are toxic for a number of insects, including carpenter ants and termites.[2]
Applications
Borates are useful for a variety of applications,[2] some of which are noted below.
- Farmers may use borate fertilizers to compensate for insufficient boron concentrations in the soil, thereby enhancing crop yields.
- Sodium borate pentahydrate (Na2B4O7 • 5H2O) is used in large amounts in making insulating fiberglass and sodium perborate bleach.
- Sodium borate decahydrate (Na2B4O7 • 10H2O, or borax) is used in laundry detergents, antiseptics, adhesives, and anti-corrosion systems, among other products.
- Borosilicate glass is used for heat-resistant cookware.
- Borates are used in ceramic and enamel glazes to increase their durability and shine.
- Various forms of borate (such as disodium octaborate tetrahydrate) are useful as fungicides and wood preservatives, protecting wood from termite attack.
- Borates may be added to cosmetics and other personal care products to control the growth of bacteria.
- Zinc borates are added to polymers to serve as flame retardants.
See also
Notes
ReferencesISBN links support NWE through referral fees
- Chang, Raymond. 2006. Chemistry, 9th ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
- Cotton, F. Albert, and Geoffrey Wilkinson. 1980. Advanced Inorganic Chemistry, 4th ed. New York: Wiley. ISBN 0471027758
- Greenwood, N.N., and A. Earnshaw. 1998. Chemistry of the Elements, 2nd ed. Oxford, UK: Burlington, MA: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654
- Holleman, Arnold Frederick, Egon Wiberg, and Nils Wiberg. 2001. Inorganic Chemistry. San Diego, CA: Academic Press. ISBN 0123526515
External links
- Borates. IMA Europe. Retrieved January 11, 2009.
- Non-CCA Wood Preservatives: Borates. National Pesticide Information Center. Retrieved January 11, 2009.
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