Borax
From Wikipedia, the free encyclopedia
- For other uses, see Borax (disambiguation).
| Borax | |
|---|---|
 |
|
| General | |
| Systematic name | Sodium tetraborate
decahydrate |
| Molecular formula | Na2B4O7·10H2O |
| Molar mass | 381.37 g/mol |
| Appearance | white solid |
| CAS number | [1303-96-4] |
| Properties | |
| Density and phase | 1.73 g/cm³, solid |
| Solubility in water | 5.1 g/100 ml (20 °C) |
| Melting point | 75 °C |
| Boiling point | 320 °C |
| Basicity (pKb) | see text |
| Structure | |
| Coordination geometry |
? |
| Crystal structure | Monoclinic |
| Thermodynamic data | |
| Std enthalpy of formation ΔfH |
-3276.75 kJ/mol |
| Standard molar entropy S |
189.53 J·K−1·mol−1 |
| Hazards | |
| MSDS | External MSDS |
| EU classification | not listed |
| NFPA 704 |
0
1
0
|
| 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 | |
| Other anions | Sodium aluminate
Sodium gallate |
| Other cations | Potassium tetraborate |
| Related compounds | Boric acid |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
|
Borax, also called sodium borate, or 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 is used in detergents and cosmetics, as an ingredient in enamel glazes, glass, pottery, and ceramics, to make buffer solutions in biochemistry, as a fire retardant and anti-fungal compound for fibreglass and cellulose insulation and as an ingredient of Slime, as an insecticide to kill ants and fleas, as a flux in metallurgy, and as a precursor for sodium perborate monohydrate that is used in detergents, as well as for boric acid and other borates. 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.
Contents |
[edit] Name
The origin of the name is traceable to the Persian word bürah (also spelled būraq or bauraq بورق) which in turn comes from Middle Persian burag [1]. The word was also used disparagingly in the 1940s to refer to tawdry modernistic furniture and other works of industrial design. Some say that the use came from advertisement displays for the household cleaner, though the use may also derive from the Yiddish word "borachs," meaning rented furniture.
[edit] Natural sources
Borax occurs naturally in evaporite deposits produced by the repeated evaporation of seasonal lakes (see playa). The most commercially important deposits are found in Turkey and near Boron, California and other locations in the American southwest, the Atacama desert in Chile, and in Tibet. Borax can also be produced synthetically from other boron compounds.
[edit] Food additive
Borax is used as a food additive in some countries with the E number E285, but is banned in the United States. Its use is similar to salt, and it appears notably in French and Iranian caviar.
[edit] Toxicity
Boric acid, sodium borate, and sodium perborate are estimated to have a fatal dose from 0.1 to 0.5g/kg (Handbook of Poisoning, Robert H. Dreisback,eight edition,p.314). These substances are toxic to all cells, and have a slow excretion rate through the kidneys. Kidney toxicity is the greatest, with liver fatty degeneration, cerebral edema, and gastroenteritis. Boric acid solutions used as an eye wash or abraded skin is known to be especially toxic to infants, especially after repeated use due to its slow elimination rate(Goodman and Gillman's: The Pharmacological Basis of Therapeutics, 6th edition,chapter on Antiseptics and Disinfectants, page 971).
[edit] Chemistry
![The structure of the anion [B4O5(OH)4]2− in borax](../../../upload/shared/thumb/9/99/Tetraborate-ion-3D-vdW.png/150px-Tetraborate-ion-3D-vdW.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. If left exposed to dry air, it slowly loses its water of hydration and becomes the white and chalky mineral tincalconite (Na2B4O7·5H2O).
[edit] Buffer
Sodium borate is used in biochemical and chemical laboratories to make buffer solutions, e.g. for gel electrophoresis of DNA. It has a lower conductivity, produces sharper bands, and can be run at higher speeds than can gels made from TBE Buffer or TAE Buffer (5 - 35 V/cm as compared to 5 - 10 V/cm). At a given voltage, the heat generation and thus the gel temperature is much lower than with TBE or TAE buffers, therefore the voltage can be increased to speed up electrophoresis so that a gel run takes only a fraction of the usual time. Downstream applications, such as isolation of DNA from a gel slice or Southern blot analysis, work as expected with sodium borate gels.
Lithium borate is similar to sodium borate and has all of its advantages, but permits use of even higher voltages due to the lower conductivity of lithium ions as compared to sodium ions. (Analytical Biochemistry 2004; 333: 1-13). However, lithium borate is much more expensive.
[edit] Flux
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.
[edit] See also
- Buffer solution
- Borax bead test
- Sodium borohydride
- Ulexite
- Twenty-Mule-Team Borax
- Francis Marion Smith
- John Veatch
