It is also known as orthopedic acid.

Preparation
It is obtained by adding calculated quantity of hydrochloric acid to a hot concentrated solution of borax (Na₂B₄O.10H₂O). The resulting solution is allowed to cool when crystals of boric acid are obtained.

Na₂B₄O₇ + 2HCI + 5H₂O  →  2NaCI + 4H₃BO₃

Properties
(i)    It is a flaky, white crystalline substance in which BO₃ units are joined by unsymmetrical H bonds as shown in. There is only weak interaction between the different layers which accounts of its low density, 1.48 g cm^-3 and easy cleavage.

(ii)    It is a weak monobasic acid and its acid properties are manifested in terms of OH^- ion acceptance (as a Lewis acid) rather than H⁺ (proton) donation. i.e., it does not act as a Bronsted acid.

B(OH)₃ + 2H₂O  <==> H₃O+ + B(OH)₄^-; pK = 9.25

(iii)    Partial dehydration of boric acid yields metaboric- acid, HBO₃ which exists in different crystalline forms.
                                                                         Rapid
HBO₂  →    B(OH)₃    →           HBO₂          →                 HBO₂
(cubic)  170⁰C   140⁰C    (molnoclinic)  (quenching) orthorhombic)

Boric acid on heatin to red heat gies B₂O₃
          red not
2H₃BO₃  →   B₂O₃ + 3H₂O
(iv)    Being a weak acid, it is difficult to titrate boric acid against sodium hydroxide as the end-point cannot be located correctly. However, it can be successfully titrated in the presence of polyhydroxy alcohols (e.g. glycerol. mannitol, catechol or sugar) which greatly enhance the acidity of boric acid. Boron is complexed by these compoin. These complex ions cannot interact with H⁺ as boron atom has already acquired its maximum covalence of four. Consequently, boric acid in presence of polthydroxy alcohols can be titrated against strong bases like NaOH to a definite end point.

(v)    When boric acid is heated with C₂H₅OH and conc. H₂SO₄, volatile triethyborate obtained. This ester burns with a green flame.
                           Cone H₂SO₂
H₃BO₃ + 3C₂H₅OH      →    (C₂H₅)₃ BO₃ + 3H₂O

(vi)    When boric acid is reacted with KHF₂ (KF,HF), KBF₄ salt is produced.

2KHF₂ + H₃BO₃    →   KBF₄ + KOH + 2H₂O
                      Potassium
                      Fluoroborate

(vii)    When H₃BO₃ is heated with CaF₂ and conc. H₂SO₄, boron trifluoride is formed

3CaF₂ + 3H₂SO4 + 2H₃BO₃ → 3CaSO₄ → 3CaSO₄ + 2BF₃ +6H₂O

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