Sodium tetraborate

Sodium tetraborate ;
Names:	sodium tetraborate; disodium tetraborate; sodium borate; borax; tincal; tincalconite; Е285 food additive;
Formula:	Na2B4O7 (anhydrous); Na2B4O7 · 5H2O (pentahydrate); Na2B4O7 · 10H2O (decahydrate);
Molar mass:	201.217 g/mol (anhydrous); 291.291 g/mol (pentahydrate); 381.366 g/mol (decahydrate);
Density:	2.37 g/cm3 (anhydrous); 1.815 g/cm3 (pentahydrate); 1.71 g/cm3 (decahydrate);
Crystal system:	monoclinic (anhydrous); a=5.507 Å, b=17.796 Å, c=8.377 Åα=90°, β=96.566°, γ=90°; orthorhombic (pentahydrate); α=90°, β=90°, γ=90°; monoclinic (decahydrate); a=11.884 Å, b=10.602 Å, c=12.2111 Åα=90°, β=106.79°, γ=90°;
Shapes:	https://en.crystalls.info/w/uploads/media/f/f6/Prolongated_hexagonal_flat_prism.json Prolongated hexagonal flat prism https://en.crystalls.info/w/uploads/media/3/37/Octahedron.json Octahedron https://en.crystalls.info/w/uploads/media/8/8f/Tetragonal_pyramid.json Tetragonal pyramid ;
Color:	colorless;
Melting point:	742 °C1,015.15 K <br />1,367.6 °F <br />1,827.27 °R <br /> (anhydrous); 140 °C413.15 K <br />284 °F <br />743.67 °R <br /> (pentahydrate);
Decomposition point:	1575 °C1,848.15 K <br />2,867 °F <br />3,326.67 °R <br /> (anhydrous);
Refractive index:	1.462 (decahydrate); 1.468 (pentahydrate);
Magnetic properties:	diamagnetic;
Stability:	slightly erodes (decahydrate); stable (pentahydrate);
Hardness:	relatively strong; (2 on Moh's scale);
Toxicity:	non-toxic; LD50=10000mg/kg

Description

Inorganic compound, salt of alkaline metal sodium and inorganic tetraboric acid. From water solutions crystallizes as decahydrate and pentahydrate.

Where to buy

Can be bought in pharmacy ("borax" as powder or glycerol solution).

Precursors

Reaction between baking soda, sodium carbonate or hydroxide and boric acid

Chemical equation:

4H₃BO₃ + 2NaHCO₃ = Na₂B₄O₇ + 7H₂O + 2CO₂↑

4H₃BO₃ + Na₂CO₃ = Na₂B₄O₇ + 6H₂O + CO₂↑

4H₃BO₃ + 2NaOH = Na₂B₄O₇ + 7H₂O

For preparation of 100.00g of sodium tetraborate

decahydratedecahydrate
pentahydrate
anhydrous

а 44.06g of soda or 27.79g of carbonate or 20.98g of sodium hydroxide and 64.85g of boric acid is required.

Add acid to the flask, then add small parts of sodium compound with stirring until heating will stop (attention, the solution may boil!) or, if you use carbonate, until carbon dioxide emission will stop. After reaction will stop, filter the solution and use it for crystal growing.

Influence of temperature

Very slow crystallization and low transparency at room temperature, but growing from hot solution eliminates these drawbacks. If temperature is over decahydrate decomposition temperature, a pentahydrate crystallization starts with another crystalline final form.

Influence of impurities

Effect of various organic dyes on the shape of sodium tetraborate crystalsSodium tetraborate

Notes

Crystal can thicken after several months due to eroding.

Storage conditions

Keep in its original form or under several layers of varnish at average humidity and room temperature. Do not keep crystals near heaters.

Solubility

TableGraph

Temperature	g/`100,00` g water			g/`100,00` g ethanol	g/`100,00` g methanol	g/`100,00` g acetone	g/`100,00` g glycerol	g/`100,00` g ethyl acetate	g/`100,00` g ethylene glycol
Temperature	(anhydrous)	(pentahydrate)	(decahydrate)	(decahydrate)	(decahydrate)	(decahydrate)	(decahydrate)	(decahydrate)	(decahydrate)
0°C273.15 K <br />32 °F <br />491.67 °R <br />	`1.11`		`2.04`
10°C283.15 K <br />50 °F <br />509.67 °R <br />			`3.19`
15°C288.15 K <br />59 °F <br />518.67 °R <br />			`3.94`	`2.54`
20°C293.15 K <br />68 °F <br />527.67 °R <br />			`4.94`				`110.97`
25°C298.15 K <br />77 °F <br />536.67 °R <br />			`6.16`		`24.84`	`0.6`		`0.14`	`71.23`
30°C303.15 K <br />86 °F <br />545.67 °R <br />			`7.76`
40°C313.15 K <br />104 °F <br />563.67 °R <br />			`12.64`
50°C323.15 K <br />122 °F <br />581.67 °R <br />		`15.87`	`21.82`
60°C333.15 K <br />140 °F <br />599.67 °R <br />			`43.53`
70°C343.15 K <br />158 °F <br />617.67 °R <br />		`20`	`58.58`
80°C353.15 K <br />176 °F <br />635.67 °R <br />		`23`	`79.57`
90°C363.15 K <br />194 °F <br />653.67 °R <br />		`28`	`113.58`
100°C373.15 K <br />212 °F <br />671.67 °R <br />	`52.5`	`35`	`191.04`

Gallery

Growing from hot solutionSodium tetraborate, Dmitry Shintyakov, VKontakteDmitry ShintyakovVKontakte
Growing from hot solutionSodium tetraborate, Gleb Vertyankin, VKontakteGleb VertyankinVKontakte
Growing at room temperatureSodium tetraborate, Rostislav Dolgikh, VKontakteRostislav DolgikhVKontakte
Growing at room temperatureSodium tetraborate, Rostislav Dolgikh, VKontakteRostislav DolgikhVKontakte
Growing from hot solutionSodium tetraborate, Dmitry Shintyakov, VKontakteDmitry ShintyakovVKontakte
Growing at room temperatureSodium tetraborate, Maxim Martinov, VKontakteMaxim MartinovVKontakte

Video

Sources

Borates
Ammonium tetraborate ((NH₄)₂B₄O₇O) • Boric acid (H₃BO₃) • Copper(II) metaborate (Cu(BO₂)₂ · H₂O) • Sodium tetraborate (Na₂B₄O₇)

Sodium compounds
Salts	Sodium acetate (NaCH₃COO) • Sodium bromide (NaBr) • Sodium citrate (Na₃C₃H₅O(COO)₃) • Sodium chlorate (NaClO₃) • Sodium chloride (NaCl) • Sodium cyclamate (C₆H₁₂NNaO₃S) • Sodium decavanadate (Na₆V₁₀O₂₈) • Sodium ethilate (NaC₂H₅O) • Sodium glutamate (NaC₅H₈NO₄) • Sodium hydrocarbonate (NaHCO₃) • Sodium hydrosulfate (NaHSO₄) • Sodium iodide (NaI) • Sodium metavanadate (NaVO₃) • Sodium niobate (NaNbO₃) • Sodium nitrate (NaNO₃) • Sodium oxalate (Na₂C₂O₄) • Sodium para-aminosalicylate (C₇H₆NNaO₃) • Sodium perchlorate (NaClO₄) • Sodium saccharinate (C₇H₄NaNO₃S) • Sodium sulfate (Na₂SO₄) • Sodium sulfide (Na₂S) • Sodium tetraborate (Na₂B₄O₇) • Sodium thiosulfate (Na₂S₂O₃) • Sodium trichloroacetate (NaCCl₃COO) • Sodium trioxalatoaluminate (Na₃[Al(C₂O₄)₃]) • Sodium tungstate (Na₂WO₄)
Double salts	Potassium-sodium tartrate (KNaC₄H₄O₆) • Sodium-ammonium sulfate (NaNH₄SO₄) • Uranyl-sodium acetate (NaUО2(CH₃COO)₃) • Uranyl-zinc-sodium acetate (NaZn(UO₂)₃(CH₃COO)₉) • Zinc-sodium sulfate (Na₂Zn(SO₄)₂)
Adducts	Glucose and sodium bromide adduct (2C₆H₁₂O₆ · NaBr) • Glucose and sodium chloride adduct (2C₆H₁₂O₆ · NaCl) • Urea and sodium chloride adduct (CO(NH₄)₂ · NaCl)
Complex compounds	Sodium dicarbonatocuprate(II) (Na₂[Cu(CO₃)₂]) • Sodium dioxalatocuprate(II) (Na₂[Cu(C₂O₄)₂]) • Sodium ethylenediaminetetraacetate-ferrate(III) (Na[Fe((OOCCH₂)₂N(CH₂)₂N(CH₂COO)₂)]) • Sodium hexacyanoferrate(II) (Na₄[Fe(CN)₆]) • Tripotassium-sodium hexacyanoferrate(II) (K₃Na[Fe(CN)₆]) • Sodium hexafluorosilicate (Na₂[SiF₆]) • Sodium nitroprusside (Na₂[Fe(CN)₅NO]) • Sodium trioxalatochromate(III) (Ns₃[Cr(C₂O₄)₃]) • Dipotassium-sodium trioxalatoferrate(III) (K₂Na[Fe(C₂O₄)₃]) • Potassium-sodium trioxalatoferrate(III) (K₅Na[Fe(C₂O₄)₃]₂) • Sodium trioxalatoferrate(III) (Na₃[Fe(C₂O₄)₃])

Sodium tetraborate
Names:	sodium tetraborate disodium tetraborate sodium borate borax tincal tincalconite Е285 food additive
Formula:	Na₂B₄O₇ (anhydrous) Na₂B₄O₇ · 5H₂O (pentahydrate) Na₂B₄O₇ · 10H₂O (decahydrate)
Molar mass:	201.217 g/mol (anhydrous) 291.291 g/mol (pentahydrate) 381.366 g/mol (decahydrate)
Density:	2.37 g/cm³ (anhydrous) 1.815 g/cm³ (pentahydrate) 1.71 g/cm³ (decahydrate)
Crystal system:	monoclinic (anhydrous) a=5.507 Å, b=17.796 Å, c=8.377 Åα=90°, β=96.566°, γ=90° orthorhombic (pentahydrate) α=90°, β=90°, γ=90° monoclinic (decahydrate) a=11.884 Å, b=10.602 Å, c=12.2111 Åα=90°, β=106.79°, γ=90°
Shapes:	Prolongated hexagonal flat prism Octahedron Tetragonal pyramid
Color:	colorless
Melting point:	742 °C1,015.15 K <br />1,367.6 °F <br />1,827.27 °R <br /> (anhydrous) 140 °C413.15 K <br />284 °F <br />743.67 °R <br /> (pentahydrate)
Decomposition point:	1575 °C1,848.15 K <br />2,867 °F <br />3,326.67 °R <br /> (anhydrous)
Refractive index:	1.462 (decahydrate) 1.468 (pentahydrate)
Magnetic properties:	diamagnetic
Stability:	slightly erodes (decahydrate) stable (pentahydrate)
Hardness:	relatively strong (2 on Moh's scale)
Toxicity:	non-toxic LD₅₀=10000mg/kg