Boric acid

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Boric acid
Boric acid wiki.jpg
Boric acid. From Wikipedia
IUPAC name
Boric acid
Other names
Boracic acid
Boron trihydroxide
Boron(III) hydroxide
Orthoboric acid
Molar mass 61.83 g/mol
Appearance White solid
Odor Odorless
Density 1.435 g/cm3
Melting point 170.9 °C (339.6 °F; 444.0 K)
Boiling point 300 °C (572 °F; 573 K) (decomposition)
2.52 g/100 ml (0 °C)
4.72 g/100 ml (20 °C)
5.7 g/100 ml (25 °C)
19.10 g/100 ml (80 °C)
27.53 g/100 ml (100 °C)
Solubility Soluble in ethanol, methanol
Moderately soluble in ethylene glycol, glycerol, pyridine
Slightly soluble in acetone, ethyl acetate
Solubility in ethanol 9.44 g/100 ml (25 °C)
Solubility in methanol 17.39 g/100 ml (25 °C)
Vapor pressure ~0 mmHg
Acidity (pKa) 9.24, 12.4, 13.3
Safety data sheet Sigma-Aldrich
Lethal dose or concentration (LD, LC):
2,660 mg/kg (rat, oral)
Related compounds
Related compounds
Boron trioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Boric acid (H3BO3) is the most readily available boron compound.



Boric acid is quoted as being "an acid by name only" and is even too weak to react with solids such as copper carbonate. It does not produce protons in water: it instead sequesters hydroxide ions from solution, forming H3O and B(OH)4-

Boric acid heated above 300 °C loses water to eventually form boron trioxide, which can be used in a thermite reaction with magnesium to produce elemental boron. Magnesium diboride is also produced as side product.

4 H3BO3 + 7 Mg → 2 B + MgB2 + 6 MgO + 6 H2O

It forms a trimethyl borate ester with methanol, which burns a brilliant green, and similarly forms triethyl borate with ethanol, which also burns green.

Reaction with alkali hydroxides will form the borate salts.

Boric acid reacts in alcoholic solution with two molecules of curcumin to form rosocyanine, a dark green ionic solid that forms deep red solutions.


Boric acid is only moderately soluble in water. It is also slightly soluble in lower alcohols and acetone.


The easiest mode of acquisition is in department or hardware stores, where it is sold in relatively pure form as roach killer or other pesticides. Boric acid is also sold in pharmacies.

Lastly, it can also be very cheaply purchased online or from lab suppliers.


Mixing hydrochloric acid and borax will form boric acid, which, due to its low solubility will precipitate out in cold water.




As it is a very weak acid, boric acid is non-corrosive, though it may irritate. Boric acid should not be consumed or inhaled in large amounts. Long term exposure should be limited.

Boric acid kills insects readily - it is often marketed as roach killer.


No special storage is required. Can be kept in any clean bottle or bag.


Small amounts of boric acid can be poured down the drain, as is poses little toxicity to the environment. Larger quantities should be taken to disposal facilities. Waste boric acid can also be used as insecticide.


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