Question

The correct statement(s) for orthoboric acid is/are:

• A. It behaves as a weak acid in water due to self ionization.
• B. It is a weak electrolyte in water.
• C. Acidity of its aqueous solution increases upon addition of ethylene glycol.
• D. It has a three dimensional structure due to hydrogen bonding.

Answer 1

Answer: (B), (C)

(A) It does not undergo self ionisation in water but accepts an electron pair from water, so it behaves as weak monobasic acid. Hence, (A) is incorrect.

$H_{3}B{O}_3+H-OH\rightleftharpoons B(OH{)}_4^{-}+H^{+}$ ... (i)

(B) When treated with 1, 2-dihydroxy or polyhydroxy compounds, they form chelate (ring complex) which effectively removes $\left[B\right(OH{)}_4^{-}]$ species from solution and thereby produce a maximum number of $H_3{O}^{+}$ or $H^{+}$ ions, i.e. results in increased acidity.

(C) Boric acid crystallises in a layer structure in which planar triangular $B{O}_3^{3-}$ ions are bonded together through hydrogen bonds.

(D) H${}_3$BO${}_3$ is a weak electrolyte in water as in water the pKa value of $H_{3}B{O}_3$ is 9.25.