1)

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


A) It behaves as a weak acid in water due to self ionisation

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:

Option B,D

Explanation:

(a) It does not undergo self ionisation  in water but accepts  an electron pair from water  so it behaves as a weak monobasic acid

  $H_{3}BO_{3}+H_{2}O\rightleftharpoons B(OH)_{4}^{-}+H^{+}$

 Hence, (a) is incorrect.

  (b)  When treated with 1,2 -dihydroxy or polyhydroxy compounds, they form chelate  (ring complex)  with effectively remove [B(OH)4]-    species from solution and thereby produce the maximum number of H3O+ or H+ ions. i,e, results in increased acidity.

(c) Baric acid crystallises in a layer structure in which planar triangular BO33- ions are bonded together through hydrogen bonds.

2232021710_tri.JPG

 (d)  In water the pKa value  of H3BO3 is 9.25

$H_{3}BO_{3}+H_{2}O\rightleftharpoons B(OH)_{4}^{-}+H^{+}:pK_{a}=9.25$

 So, it is weak electrolyte in water