p-Block Elements-I - Result Question 14

####14. The correct statement(s) for orthoboric acid is/are(2014 Adv.)

(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

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Answer:

Correct Answer: 14. (a,b,c)

Solution:

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

H3BO3+H2OB(OH)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] species from solution and thereby produce maximum number of H3O+or H+ ions, i.e. results in increased acidity.

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

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

H3BO3+H2OB(OH)4+H+;pKa=9.25

So, it is a weak electrolyte in water.



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