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

Question

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

Tardigrade Admin · Accepted Answer

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

H_{3} B O_{3} + H_{2} O ⇌ B (O H)_{4}^{-} + H^{+}

Hence, (a) is incorrect.
(b) When treated with

1, 2

-dihydroxy or polyhydroxy compounds, they form chelate (ring complex) which effectively remove

[B (O H)_{4}]^{-}

species from solution and thereby produce 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) In water the

p K_{a}

value of

H_{3} B O_{3}

is

9.25

.

H_{3} B O_{3} + H_{2} O ⇌ B (O H)_{4}^{-} + H^{+}; p K_{a} = 9.25

So, it is a weak electrolyte in water.

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

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

Acidity of its aqueous solution increases upon addition of ethylene glycol

It has a three-dimensional structure due to hydrogen bonding

It is a weak electrolyte in water