Boric acid

Boric acid, also called boracic acid or orthoboric acid, is a mild acidoften used as an antiseptic, insecticide, flame retardant, and as a precursor of other chemical compounds. It exists in the form of colorless crystals or a white powder and dissolves in water. It has the chemical formulaH₃BO₃, sometimes written B(OH)₃.

Preparation

Boric acid is produced mainly from borate minerals by the reaction with sulfuric acid. The largest source of borates in the world is an open-pit minein Death Valley, California, USA.

Properties

Boric acid is soluble in boiling water. When heated above 170°C it dehydrates, forming metaboric acid HBO₂. Metaboric acid is a white, cubic crystalline solid and is only slightly soluble in water. It melts at about 236°C, and when heated above about 300°C further dehydrates, forming tetraboric acid or pyroboric acid, H₄B₄O₇. Boric acid can refer to any of these compounds. Further heating leads to boron trioxide.

Boric acid does not dissociate in aqueous solution, but is acidic due to its interaction with watermolecules:

B(OH)₃ + H₂O ⇌ B(OH)₄⁻ + H⁺

K_a = 5.8x10⁻¹⁰ L/mol; pK_a = 9.24.

Polyborate anions 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 tetraborate ion, found in the mineral borax:

4B(OH)₄⁻ + 2H⁺ ⇌ B₄O₇²⁻ + 9H₂O

Uses

It can be used as an antiseptic only for minor burns or cuts and is sometimes used in dressings or salves or is applied in a very dilute solution as an eye wash. It is poisonous if taken internally or inhaled, although it is generally not considered to be much more toxic than table salt(based on its mammal LD50rating of 2660mg/kg body mass).

Boric acid can be used to treat candidiasis(vaginal yeast infections) by filling gelcaps with boric acid powder and inserting two into the vaginal canal at bedtime for three to four nights in a row.

It is also used as prevention of athlete's foot, by inserting powder in the socks or stockings.

It is often used as a relatively nontoxic insecticide, for killing cockroaches, termites, fire ants, fleas, and many other insects. It can be used directly in powdered form for fleas and cockroaches, or mixed with sugaror grape jellyfor ants. It is also a component of many commercial insecticides. In this use, especially in the case of cockroaches, the boric acid in the form of a powder is applied to areas frequented by the insects. The lightweight particles cling to the legs of the insects and eventually cause fatal chemical burns. Boric acid for this use in residential apartments is sold commercially in urban areas afflicted with cockroaches.

In the jewelry industry, boric acid is often used in combination with denatured alcoholto reduce surface oxidation and firescale from forming on metals during annealingand solderingoperations.

Boratesincluding boric acid have been used since the time of the Greeksfor cleaning, preserving food, and other activities.

Lithium boric acidis the lithium saltof boric acid and is used in the laboratory as buffer for gel. TBE bufferis widely used for the electrophoresisof nucleic acidsand has a higher buffer capacity than a TAE Buffer. It can be used for DNAand RNApolyacrylamideand agarose gelelectrophoresis.

It used in pyrotechnicsto prevent the amide-forming reaction between aluminum and nitrates. A small amount of boric acid is added to the composition to neutralize alkaline amides that react with the aluminum.

Reference

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External links

• International Chemical Safety Card 0991
• National Pollutant Inventory - Boron and compounds
• Boric acid at ChemicalLand21cs:Kyselina boritá

de:Borsäure es:Ácido bórico fr:Acide borique ja:ホウ酸 nl:Boorzuur pl:Kwas borowy pt:Ácido bórico sv:Borsyra

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Boric+acid Wikipedia article Boric acid.