Question

Boric acid is a very weak acid but in the presence of certain organic compounds, it acts as a strong acid. Which one of the following organic compound(s) affect cannot such

(A) change?
(B) Glycerol
(C) Acetic acid
(D) Ethyl Alcohol
(E) Ethylene

Answer 1

Hint: It acts as a strong acid in presence of polyhydroxy compounds, one such compound contains three carbon atoms and one hydroxyl group is attached to each carbon atom. It is used in improving hydration. Boric acid acts as Lewis acid because it accepts lone pairs of electrons.

Complete solution step by step:
-Boric acid is a weak monobasic acid but it does not donate protons, so it is not a protonic acid.
-it acts as Lewis acid as it accepts lone pairs of electrons from hydroxyl ions. As boron has three bonds and six electrons so to complete its octet it accepts lone pairs of electrons.
-Boron itself cannot release hydrogen ion but as it receives a lone pair of electron from hydroxyl group in turn it releases hydrogen ion.

-When boric acid reacts with ethyl alcohol, it forms triethyl borate. It is an ester of boric acid and ethanol.

Boric acid acts as weak Lewis acid.

-Boric acid forms a stable cyclic complex with polyhydroxy compounds like glycerol. This helps in release of hydrogen ions.
Hence, Boric acid is a very weak acid but in the presence of certain organic compounds, it acts as a strong acid. Option (B) Acetic acid, (C)Ethyl Alcohol, (D)Ethylene Cannot affect such change.

Note: Boric acid is prepared by acidifying the solution of borax. Boric acid is sparingly soluble in water but highly soluble in hot water. Planar $B{{O}_{3}}$units are joined by hydrogen bonds and it has a layer structure. -Boron itself cannot release hydrogen ions but as it receives a lone pair of electrons from the hydroxyl group in turn it releases hydrogen ions.