In chemistry, tetraborate or pyroborate is an

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

(negative ion) with formula ; or a

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quanti ...

containing that anion, such as

sodium tetraborate Borax is a salt (chemistry), salt (ionic compound), a hydration (chemistry), hydrated borate of sodium, with chemical formula often written . It is a colorless crystalline solid, that dissolves in water to make a base (chemistry), basic aqueo ...

, . It is one of the boron

oxoacid An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bonded to oxygen that can dissociate to produce ...

s, that is, a

borate A borate is any of several boron oxyanions, negative ions consisting of boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt with such anions, such as sodium metaborate, and disodium tetraborate . The name a ...

. The name is also applied to the hydrated ion as present in

borax Borax is a salt (chemistry), salt (ionic compound), a hydration (chemistry), hydrated borate of sodium, with chemical formula often written . It is a colorless crystalline solid, that dissolves in water to make a base (chemistry), basic aqueo ...

The ion occurs in

boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolve ...

solutions at neutral pH, being formed by condensation of orthoborate and tetrahydroxyborate anions: : 2 B(OH)₃ + 2 ⇌ + 5 H₂O The tetraborate anion (

tetramer A tetramer () (''tetra-'', "four" + '' -mer'', "parts") is an oligomer formed from four monomers or subunits. The associated property is called ''tetramery''. An example from inorganic chemistry is titanium methoxide with the empirical formula T ...

) includes two tetrahedral and two trigonal boron atoms symmetrically assembled in a fused bicyclic structure. The two tetrahedral boron atoms are linked together by a common oxygen atom, and each also bears a negative net charge brought by the supplementary OH⁻ groups laterally attached to them. This intricate molecular anion also exhibits three rings: two fused distorted hexagonal (boroxole) rings and one distorted octagonal ring. Each ring is made of a succession of alternate boron and oxygen atoms. Boroxole rings are a very common structural motif in polyborate ions. The hydrated tetraborate anion occurs in the mineral

(sodium tetraborate octahydrate) with the formula Na₂ ₄O₅(OH)₄�8H₂O. The borax chemical formula is also commonly written in a more compact notation as Na₂B₄O₇·10H₂O. Sodium borate can be obtained in high purity and so can be used to make a

standard solution In analytical chemistry, a standard solution is a solution containing a precisely known concentration of an element or a substance. A known mass of solute is dissolved to make a specific volume. It is prepared using a standard substance, such as a ...

in titrimetric analysis..

References

Anions Salts Sodium Borates {{chem-stub