NEET Practice Questions (MCQs) with Answers & Solutions

Boric acid (H₃BO₃) is polymeric due to the presence of hydrogen bonds. The hydrogen atoms present in the boric acid molecule can form hydrogen bonds with the oxygen atoms of other boric acid molecules, leading to a polymeric structure.

 Boric acid is obtained by treating a hot concentrated solution of borax with hydrochloric acid or sulphuric acid. The resulting solution on concentration and cooling gives crystals of boric acid.

Boric acid, on heating, loses water in three different stages at different temperatures ultimately giving boron trioxide:

$$\begin{gathered} {\mathrm{H}}_3{\mathrm{BO}}_3^{-}\stackrel{100°\mathrm{C}}{\to }{\mathrm{H}}_2\mathrm{O}+{\mathrm{HBO}}_2\left(\mathrm{Metaboric} \mathrm{acid}\right) \\ 4{\mathrm{HBO}}_2^{-}\underset{\left(-{\mathrm{H}}_2\mathrm{O}\right)}{\overset{150°\mathrm{C}}{\to }}{\mathrm{H}}_2{\mathrm{B}}_4{\mathrm{O}}_7\left(\mathrm{Tetra} \mathrm{boric} \mathrm{acid}\right) \end{gathered}$$

When boron trichloride (BCl3) reacts with water (H2O), it forms boric acid (H3BO3) and hydrogen chloride (HCl) as products. The balanced chemical equation for this reaction is: BCl3 + 3H2O → H3BO3 + 3HCl

When a mineral acid is added to an aqueous solution of borax (Na2B4O7.10H2O), orthoboric acid (H3BO3) is formed. This is because the borate ions from borax are protonated by the mineral acid.