It has trigonal planar geometry due to three oxygen atoms around the boron. In this bond length of B-O is 136pm and O-H is 97pm. The structure of unit cell of boric acid is given below-
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It is a colorless or white crystalline solid at room temperature.
Its molar mass is 61.83 g/mol.
Its melting point is 170.9℃.
Its boiling point is 300℃.
It is soluble in water.
On heating boric acid gives metaboric acid. Reaction is given below –
H3BO3 170℃→ HBO2 + H2O
At 300℃, it gives tetraboric acid. Reaction is given below –
4HBO2 🡪 H2B4O7 + H2O
On heating above 330℃, it gives boron trioxide. Reaction is given below –
H2B4O7 🡪 2B2O3 + H2O
Boric acid reacts with alcohols and gives borate esters. Reaction is given below
B(OH)3 + 3ROH 🡪 B(OR)3 + 3H2O
It also dissolves in anhydrous sulfuric acid. Reaction is given below –
B(OH)3 + 6H2SO4 🡪 B(HSO4)4- + 2HSO4- + 3H3O+
By Borax - Boric acid is prepared by reaction of borax with mineral acid (or hydrochloric acid). Reaction involved is given below –
Na2B4O7.10H2O + 2HCl 🡪 4B(OH)3 + 2NaCl + 5H2O
By Hydrolysis of Diborane - Boric acid is also formed as by product of hydrolysis of diborane. Reaction involved is given below –
B2H6 + 6H2O 🡪 2B(OH)3 + 6H2
By Hydrolysis of Trihalide - Boric acid is also formed as by product of hydrolysis of boron trihalides. Reaction involved is given below –
BX3 + 3H2O 🡪 B(OH)3 + 3HX (X = Cl, Br, I)
We have been using boric acid since ancient times. Presently it is mainly used in industries. Few of its uses are listed below –
It is used in manufacturing of monofilament fiberglass.
It is used in the jewelry industry in combination with denatured alcohol.
It is used in production of glass in LCD flat panel displays.
It is used in electroplating.
Boric acid mixture is used as a fire retarding agent.
It is used in manufacturing of ramming mass.
It has medicinal uses as well such as it reduces the harmful effect of HF.
Boric acid mixed with borax is used for welding flux by blacksmiths.
It is often used as antiseptic, insecticide, flame retardant, neutron absorber etc.
It is used to prevent or destroy existing wet and dry rot in timbers.
It is used as a primary buffer system in swimming pools.
It is used in some nuclear power plants as a neutron poison.
Its mixture with petroleum or vegetable oil works as an excellent lubricant.
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