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Chemistry Question on p -Block Elements

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

It is a weak electrolyte in water

Explanation

Solution

(a) It does not undergo self ionisation in water but accepts an electron pair from water, so it behaves as weak monobasic acid. H3BO3+H2O⇌B(OH)41+H+H_3BO_3 + H_2O \rightleftharpoons B(OH)^1_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(OH)4]−[B(OH)_4]^- species from solution and thereby produce maximum number of H3O+ or H+H3O^+ \, or \, H^+ ions, i.e. results in increased acidity.
(c) Boric acid crystallises in a layer structure in which planar triangular BO33−BO^{3-}_3 ions are bonded together through hydrogen bonds.
(d) In water the pK a value of H3B 03 is 9.25.H3BO3+H2O⇌B(OH)4−+H+;pKa=9.25H_3BO_3 + H_2O \rightleftharpoons B(OH)^-_4 + H^+ ; pK_a = 9.25 So, it is a weak electrolyte in water.