Question

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

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

Answer 1

Answer: (B), (D)

It is a weak electrolyte in water.
Acidity of its aqueous solution increases upon addition of ethylene glycol.

(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.