Sodium borate

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Sodium borate is a generic name for any salt of sodium with an anion consisting of boron and oxygen, and possibly hydrogen, or any hydrate 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, (Na+)2[B4O5(OH)4]2−·8H2O = Na2B4H20O17.

The ternary phase diagram of the Na2O–B2O3–H2O phase diagram in the 0–100 °C temperature range contains 13 unique hydrated crystalline sodium borates, including five important industrial products. [1]

Sodium borates, as well as boroxy acids, are often described as mixtures xNa2O·yB2O3·zH2O = Na2xB2yH2zOx+3y+z, with x, y, and z chosen to fit the elemental formula, or a multiple thereof. Thus, for example, borax Na2B4H20O17 would be 1Na2O·2B2O3·10H2O, and boric acid B(OH)3 would be 0Na2O·1B2O3·1H2O = 2[B(OH)3].

The elemental formula was often interpreted as a z-hydrate of an "anhydrous" salt without any hydrogen, namely Na2xB2yO3y·zH2O. However, later research uncovered that many borates have hydroxyl groups HO− bound covalently to the boron atoms in the anion. Thus borax, for example, is still often described as a decahydrate Na2B4O7·10H2O, with the implied anion [B4O7]2−, whereas the correct formula is Na2B4O5(OH)4·8H2O, with anion [B4O5(OH)4]2−.

The following table gives some of the crystalline sodium borates in this family. [2] The column x/(x+y) is the formal mole fraction of Na2O in the "anhydrous" version.

x:y:zx/(x+y)Elemental formulaAs hydrateCorrect formulaName
3:1:00.750Na6B2O6 = Na3BO3Na3BO3 trisodium orthoborate (anhydrous)
1:1:00.500Na2B2O4 = NaBO2       Na3B3O6 sodium metaborate
1:1:10.500Na2H2B2O5Na2B2O4·H2O ? ? [2]
1:1:40.500Na2H8B2O8 = NaBH4O4NaBO2·2H2ONaB(OH)4 sodium tetrahydroxyborate [2]
1:1:80.500Na2H16B2O12 = NaBH8O6NaBO2·4H2O ? ? [2]
1:2:00.333Na2B4O7Na2B4O7borax (anhydrous)
1:2:40.333Na2H8B4O11Na2B4O7·4H2ONa2B4O5(OH)4borax "tetrahydrate"
1:2:50.333Na2H10B4O12 = NaB2H5O6Na2B4O7·5H2ONa2B4O5(OH)4·H2Oborax "pentahydrate" [2]
1:2:100.333Na2H20B4O17Na2B4O7·10H2ONa2B4O5(OH)4·8H2Oborax "decahydrate" [2]
1:3:00.250Na2B6O10 = NaB3O5NaB3O5 ?
1:4:00.200Na2B8O13Na2B8O13 disodium octaborate (anhydrous)
2:9:110.182Na4H22B18O31                    Na4B18O29·11H2ONa2[B8O11(OH)4]·[B(OH)3]·2H2O [1] disodium enneaborate
1:5:20.167Na2H4B10O18 = NaH2B5O9NaB5O8·H2O ? sodium pentaborate "monohydrate" [1]
1:5:40.167Na2H8B10O20 = NaH4B5O10  NaB5O8·2H2ONa[B5O7(OH)2]·H2Osodium pentaborate "dihydrate" [3]
1:5:100.167Na2H20B10O26 = NaH10B5O13NaB5O8·5H2O ?sodium pentaborate "pentahydrate" [4]
3:5:40.125Na6H8B10O22 = Na3H4B5O11Na3B5O7·2H2ONa3B5O8(OH)2·H2O trisodium pentaborate [5]

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. [6]

Some sodium borates hower cannot be analyzed as combinations xNa2O·yB2O3·zH2O of the three ordinary oxides. The most important example is sodium perborate, originally described as NaBO3·H2O but actually (Na+)2[B2O4(OH)4]2−. The anion of this compound has two peroxide bridges −O−O− which make it oxygen-rich compared to the general family above.

Related Research Articles

<span class="mw-page-title-main">Boron</span> Chemical element with atomic number 5 (B)

Boron is a chemical element. It has 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 three valence electrons for forming covalent bonds, resulting in many compounds such as boric acid, the mineral sodium borate, and the ultra-hard crystals of boron carbide and boron nitride.

<span class="mw-page-title-main">Boric acid</span> Weak acid with formula B(OH)₃

Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula B(OH)3. It may also be called hydrogen orthoborate, trihydroxidoboron or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolves in water, and occurs in nature as the mineral sassolite. It is a weak acid that yields various borate anions and salts, and can react with alcohols to form borate esters.

A borate is any of a range of boron oxyanions, anions containing boron and oxygen, such as orthoborate BO3−3, metaborate BO−2, or tetraborate B4O2−7; or any salt of such anions, such as sodium metaborate, Na+[BO2]− and borax (Na+)2[B4O7]2−. The name also refers to esters of such anions, such as trimethyl borate B(OCH3)3 but they are alkoxides.

<span class="mw-page-title-main">Borax</span> Boron compound, a salt of boric acid

Borax (also referred to as sodium borate, tincal and tincar ) is a salt (ionic compound), a hydrated or anhydrous borate of sodium, with the chemical formula Na2H20B4O17 (also written as Na2B4O7·10H2O).

<span class="mw-page-title-main">Boron trioxide</span> Chemical compound

Boron trioxide or diboron trioxide is the oxide of boron with the formula B2O3. It is a colorless transparent solid, almost always glassy (amorphous), which can be crystallized only with great difficulty. It is also called boric oxide or boria. It has many important industrial applications, chiefly in ceramics as a flux for glazes and enamels and in the production of glasses.

<span class="mw-page-title-main">Sodium aluminate</span> Chemical compound

Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as NaAlO2, NaAl(OH)4 (hydrated), Na2O·Al2O3, or Na2Al2O4. Commercial sodium aluminate is available as a solution or a solid.
Other related compounds, sometimes called sodium aluminate, prepared by reaction of Na2O and Al2O3 are Na5AlO4 which contains discrete AlO45− anions, Na7Al3O8 and Na17Al5O16 which contain complex polymeric anions, and NaAl11O17, once mistakenly believed to be β-alumina, a phase of aluminium oxide.

<span class="mw-page-title-main">Borate mineral</span> Mineral which contains a borate anion group

The Borate Minerals are minerals which contain a borate anion group. The borate (BO3) units may be polymerised similar to the SiO4 unit of the silicate mineral class. This results in B2O5, B3O6, B2O4 anions as well as more complex structures which include hydroxide or halogen anions. The [B(O,OH)4]− anion exists as well.

<span class="mw-page-title-main">Tetraborate</span>

In chemistry, tetraborate or pyroborate is an anion with formula B4O2−7; or a salt containing that anion, such as sodium tetraborate, Na2B4O7. It is one of the boron oxoacids, that is, a borate.

Sodium perborate is chemical compound whose chemical formula may be written NaH2BO4, Na2H4B2O8, or, more properly, [Na+]2[B2O4(OH)4]2−. Its name is sometimes abbreviated as PBS.

<span class="mw-page-title-main">Sodium metasilicate</span> Chemical compound

Sodium metasilicate is the chemical substance with formula Na
2SiO
3, which is the main component of commercial sodium silicate solutions. It is an ionic compound consisting of sodium cations Na+
 and the polymeric metasilicate anions [–SiO2−
3–]n. It is a colorless crystalline hygroscopic and deliquescent solid, soluble in water but not in alcohols.

Tetrahydroxyborate is an inorganic anion with the chemical formula [BH4O4]− or [B(OH)4]−. It contributes no colour to tetrahydroxyborate salts. It is found in the mineral hexahydroborite, Ca(B(OH)4)2 · 2 H2O, originally formulated CaB2O4 · 6 H2O. It is one of the boron oxoanions, and acts as a weak base. The systematic names are tetrahydroxyboranuide (substitutive) and tetrahydroxidoborate(1−) (additive). It can be viewed as the conjugate base of boric acid.

<span class="mw-page-title-main">Disodium octaborate</span> Chemical compound

Disodium octaborate is a borate of sodium, a chemical compound of sodium, boron, and oxygen — a salt with elemental formula Na2B8O13 or (Na+)2[B8O13]2−, also written as Na2O·4B2O3. It is a colorless crystalline solid, soluble in water.

<span class="mw-page-title-main">Chromium(III) sulfate</span> Chemical compound

Chromium(III) sulfate usually refers to the inorganic compounds with the formula Cr2(SO4)3.x(H2O), where x can range from 0 to 18. Additionally, ill-defined but commercially important "basic chromium sulfates" are known. These salts are usually either violet or green solids that are soluble in water. It is commonly used in tanning leather.

<span class="mw-page-title-main">Sodium metaborate</span> Chemical compound

Sodium metaborate is a chemical compound of sodium, boron, and oxygen with formula NaBO2. However, the metaborate ion is trimeric in the anhydrous solid, therefore a more correct formula is Na3B3O6 or (Na+)3[B3O6]3−. The formula can be written also as Na2O·B2O3 to highlight the relation to the main oxides of sodium and boron. The name is also applied to several hydrates whose formulas can be written NaBO2·nH2O for various values of n.

<span class="mw-page-title-main">Metaborate</span> Boron-oxygen anion or functional group

A metaborate is a borate anion consisting of boron and oxygen, with empirical formula BO−2. Metaborate also refers to any salt or ester of such anion. Metaborate is one of the boron's oxyanions. Metaborates can be monomeric, oligomeric or polymeric.

Magnesium hydroxychloride is the traditional term for several chemical compounds of magnesium, chlorine, oxygen, and hydrogen whose general formula xMgO·yMgCl2·zH2O, for various values of x, y, and z; or, equivalently, Mgx+y(OH)2xCl2y(H2O)z−x. The simple chemical formula that is often used is Mg(OH)Cl, which appears in high school subject, for example.Other names for this class are magnesium chloride hydroxide, magnesium oxychloride, and basic magnesium chloride. Some of these compounds are major components of Sorel cement.

Disodium enneaborate is the traditional name for a salt of sodium, boron, oxygen, and hydrogen, with elemental formula Na2B9H22O20 or Na2B9O9·11H2O. It is the sodium borate with the highest boron/sodium ratio.

Sodium pentaborate, more properly disodium decaborate, is a chemical compound of sodium, boron, and oxygen; a salt with elemental formula NaB5O8, Na2B10O16, or Na2O·5B2O3. It is a colorless crystalline solid, soluble in water.

Trisodium borate is a chemical compound of sodium, boron, and oxygen, with formula Na3BO3, or (Na+)3[BO3]3−. It is a sodium salt of the orthoboric acid B(OH)3.

<span class="mw-page-title-main">Sodium tetrahydroxyborate</span> Chemical compound

Sodium tetrahydroxyborate is a salt of with chemical formula NaH4BO4 or Na+[B(OH)4]−. It is one of several sodium borates. At room temperature it is a colorless crystalline solid.

References

  1. 1 2 3 Doinita Neiner, Yulia V. Sevryugina, Larry S. Harrower, and David M. Schubert (2017): "Structure and Properties of Sodium Enneaborate, Na2[B8O11(OH)4]·B(OH)3·2H2O". Inorganic Chemistry, volume 56, issue 12, pages 7175–7181. doi : 10.1021/acs.inorgchem.7b00823
  2. 1 2 3 4 5 6 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. doi : 10.1021/je60034a005
  3. ↑ S. Stella Mary, S. Shahil Kirupavathy, P. Mythili, R. Gopalakrishnan (2008): "Growth and characterization of sodium pentaborate [Na(H4B5O10)] single crystals". Spectrochimica Acta Part A, volume 71, issue 4, 15 pages 1311-1316. doi : 10.1016/j.saa.2008.04.021
  4. ↑ 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. doi : 10.1016/j.mtcomm.2022.103157
  5. ↑ Silvio Menchetti and Cesare Sabelli (1977): "The crystal structure of synthetic sodium pentaborate monohydrate". Acta Crystallographica Section B, volume B33, pages 3730-3733. doi : 10.1107/S0567740877011959
  6. ↑ 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. doi : 10.1098/rspl.1904.0112
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