Sodium borate is a generic name for any
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 quantitie ...
of
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
with 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 convent ...
consisting of
boron
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
and
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
, and possibly
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
, or any
hydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
thereof. It can be seen as a hydrated sodium salt of the appropriate
boroxy acid, although the latter may not be a stable compound.
Many sodium borates have important industrial and household applications; the best known being
borax
Borax is a salt (ionic compound), a hydrated borate of sodium, with chemical formula often written . It is a colorless crystalline solid, that dissolves in water to make a basic solution. It is commonly available in powder or granular form, ...
, = .
The
ternary phase diagram of the –– phase diagram in the 0–100 °C temperature range contains 13 unique
hydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
d crystalline sodium borates, including five important industrial products.
[
Sodium borates, as well as boroxy acids, are often described as mixtures = , with ''x'', ''y'', and ''z'' chosen to fit the elemental formula, or a multiple thereof. Thus, for example, borax would be , and ]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 dissolves ...
would be = .
The elemental formula was often intrepreted as a ''z''-hydrate of an "anhydrous" salt without any hydrogen, namely . However, later research uncovered that many borates have hydroxyl groups bound covalently to the boron atoms in the anion. Thus borax, for example, is still often described as a decahydrate , with the implied anion , whereas the correct formula is , with anion .
The following table gives some of the crystalline sodium borates in this family.[ The column ''x''/(''x''+''y'') is the formal ]mole
Mole (or Molé) may refer to:
Animals
* Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America
* Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpida ...
fraction of in the "anhydrous" version.
Some of the borates above may have more than one isomeric or crystalline form. Some may decompose when dissolved in water. Note that the anion of the "anhydrous borax" is different from that of its "hydrates".
Some of the anhydrous borates above can be crystallized from molten mixtured of sodium oxide and boric oxide.[
Some sodium borates hower cannot be analyzed as combinations of the three ordinary oxides. The most important example is ]sodium perborate
Sodium perborate is chemical compound whose chemical formula may be written , , or, more properly, ·. Its name is sometimes abbreviated as PBS (not to be confused with phosphate-buffered saline).
The compound is commonly encountered in anhydro ...
, originally described as but actually . The anion of this compound has two peroxide
In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable.
The most common peroxide is hydrogen p ...
bridges which make it oxygen-rich compared to the general family above.
References
[S. Stella Mary, S. Shahil Kirupavathy, P. Mythili, R. Gopalakrishnan (2008): "Growth and characterization of sodium pentaborate a(H4B5O10)single crystals". ''Spectrochimica Acta Part A'', volume 71, issue 4, 15 pages 1311-1316. ]
[Taha Cagri Senocak, Taha Alper Yilmaz, Hasan Feyzi Budak, Gokhan Gulten, Ahmet Melik Yilmaz, Kadri Vefa Ezirmik, Yasar Totikc (2022): "Influence of sodium pentaborate (B5H10NaO13) additive in plasma electrolytic oxidation process on WE43 magnesium alloys". ''Materials Today Communications'', volume 30, article 103157. ]
[Doinita Neiner, Yulia V. Sevryugina, Larry S. Harrower, and David M. Schubert (2017): "Structure and Properties of Sodium Enneaborate, Na2 8O11(OH)4·B(OH)3·2H2O". ''Inorganic Chemistry'', volume 56, issue 12, pages 7175–7181. ]
[Nelson P. Nies and Richard W. Hulbert (1967): "Solubility isotherms in the system sodium oxide-boric oxide-water. Revised solubility-temperature curves of boric acid, borax, sodium pentaborate, and sodium metaborate". ''Journal of Chemical and Engineering Data'', volume 12, issue 3, pages 303–313. ]
[Charles Hutchens Burgess and Alfred Holt (1905): "Some physical characters of the sodium borates, with a new and rapid method for the determination of melting points." ''Proceedings of the Royal Society of London, volume 74, pages 285–295.]
[Silvio Menchetti and Cesare Sabelli (1977): "The crystal structure of synthetic sodium pentaborate monohydrate". ''Acta Crystallographica Section B'', volume B33, pages 3730-3733. ]
{{Chemistry index
sodium compounds
borates