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IUPAC name
Sodium tetraborate decahydrate
Systematic IUPAC name
Sodium borate
Other names
Disodium tetraborate
Sodium tetraborate
Na2B4O7 (anhydrous)
Na2B4O7·10H2O (decahydrate)
Molar mass 381.38 g/mol (decahydrate)
201.22 g/mol (anhydrate)
Appearance White crystalline solid
Odor Odorless
Density 1.73 g/cm3
Melting point 743 °C (1,369 °F; 1,016 K) (anhydrous)
Boiling point 1,575 °C (2,867 °F; 1,848 K)
2.7 g/100 ml (20 °C)[1]
Solubility Soluble in ethylene glycol, glycerol
Moderate soluble in diethylene glycol, methanol
Slightly soluble in acetone, ethanol, ethyl acetate
Vapor pressure ~0 mmHg
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Related compounds
Related compounds
Boric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Borax or sodium borate, sodium tetraborate, is an important boron compound. It has the chemical formula Na2B4O7.



Sodium borate will react with a strong acid to release boric acid.

Na2B4O7·10H2O + 2 HCl → 4 H3BO3 + 2 NaCl + 5 H2O

Addition of hydrogen peroxide, sodium hydroxide to sodium borate pentahydrate will give sodium perborate.

Na2B4O7·5 H2O + NaOH + 2 H2O2 → Na2B2O4(OH)4 + NaOH + 5 H2O + 3/2 O2

When borax is added to a flame, it gives a yellow-green color. Since the yellow flame of sodium is undesired, boric acid is used in fireworks instead of borax for green flame and as solution in methanol for pure green flames.

Borax is a prime material in the manufacturing of borosilicate glass. Unlike boric acid, it is not volatile and can be used in high temperature chemical reactions as a source of boron.


Borax is a white crystalline solid. It is odorless, and has an unpleasant taste. Borax melts at 743 °C and boils at 1,575 °C. It has a density of 1.73 g/cm3. Borax is poorly soluble in cold water, but it's solubility increases with temperature. It is soluble in some organic solvents, like ethylene glycol, glycerol, while moderate soluble in diethylene glycol, methanol. Borax is only slightly soluble in more common solvents like acetone, ethanol, ethyl acetate.

Water solubility of borax


Borax is sold by various chemical suppliers. Can also be acquired online.

It is also sold in various pharmacies and iron forgeries.


Sodium borate can be made by reacting boric acid with sodium hydroxide, under continuous stirring.

4 H3BO3 + 2 NaOH → Na2B4O7 + 7 H2O


  • Make boric acid
  • Grow borax crystals, borax snowflakes
  • pH buffer
  • Water-softening agent
  • Flux for melting metals
  • Borax method (gold extraction)
  • Fire retardant
  • Make sodium perborate
  • Curing agent (leather)



Borax has low toxicity. It is only mildly irritant to skin.

Borax was added to the Substance of Very High Concern (SVHC) candidate list on 16 December 2010 in the EU.


Borax should be stored in closed bottles


Sodium tetraborate can be dumped in trash.



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