Boric acid
| Boric acid
|
|
|
| General
|
| Other names
| Orthoboric acid
Boracic acid
Optibor®
Borofax®
|
| Molecular formula
| H3BO3
|
| Molar mass
| 61.83 g/mol
|
| Appearance
| white crystalline solid
|
| CAS number
| [10043-35-3]
|
| Properties
|
| Density and phase
| 1.435 g/cm3, solid
|
| Solubility in water
| 5.7 g/100 ml (25°C)
|
| Melting point
| 169°C decomp.
|
| Acidity (pKa)
| 9.24 (see text)
|
| Structure
|
| Molecular shape
| planar
|
| Crystal structure
| ?
|
| Dipole moment
| zero
|
| Thermodynamic data
|
Standard enthalpy
of
formation ΔfHosolid
| −1093.99 kJ/mol
|
Standard molar entropy
Sosolid
| 88.7 J.K−1.mol−1
|
| Hazards
|
| MSDS
| External MSDS
|
| EU classification
| not listed
|
| NFPA 704
|
|
| Flash point
| non-flammable
|
| Supplementary data page
|
Structure and
properties
| n, εr, etc.
|
Thermodynamic
data
| Phase behaviour
Solid, liquid, gas
|
| Spectral data
| UV, IR, NMR, MS
|
| Related compounds
|
| Related compounds
| Boron trioxide
Borax
|
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
Infobox disclaimer and references
|
Boric acid, also called boracic acid or orthoboric acid, is a mild acid often 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 formula H3BO3, 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 mine in 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 water molecules:
- B(OH)3 + H2O ⇌ B(OH)4− + H+
- Ka = 5.8x10−10 L/mol; pKa = 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 LD50 rating of 2660).
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 sugar for 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 alcohol to reduce surface oxidation and firescale from forming on metals during annealing and soldering operations.
Borates including boric acid have been used since the time of the Greeks for cleaning, preserving food, and other activities.
Lithium boric acid is the lithium salt of boric acid and is used in the laboratory as buffer for gel. TBE buffer is widely used for the electrophoresis of nucleic acids and has a higher buffer capacity than a TAE Buffer. It can be used for DNA and RNA polyacrylamide and agarose gel electrophoresis.
Reference
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External links
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