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Question: Which of the following compounds is protonic acid? A. \(S{O_2}{(OH)_2}\) B. \(B{(OH)_3}\) C. \...

Which of the following compounds is protonic acid?
A. SO2(OH)2S{O_2}{(OH)_2}
B. B(OH)3B{(OH)_3}
C. PO(OH)3PO{(OH)_3}
D. SO(OH)2SO{(OH)_2}

Explanation

Solution

The term protonic is used to distinguish traditional acids from lewis acids from lowry-Bronsted acids in non-aqueous solvent. It produces H+{H^ + } ion in the aqueous solutions.

Complete step by step answer: Let’s discuss each of the above options to find out the correct answer.
In aqueous solutions H2SO4{H_2}S{O_4} (sulphuric acid) ionizes completely to form hydronium ions (H3O+)({H_3}{O^ + }) and hydrogen sulphate ions (HSO4−)(HSO_4^ - ). Since it is a strong mineral acid and in dilute solutions, hydrogen sulphate ions also dissociate to give hydronium ions and sulphate ions as :
H2SO4(aq)→H3O++HSO4− HSO4−→H3O++SO42−  {H_2}S{O_4}(aq) \to {H_3}{O^ + } + HSO_4^ - \\\ HSO_4^ - \to {H_3}{O^ + } + SO_4^{2 - } \\\
Hence we can say it is protonic acid.
Now in the case of B(OH)3B{(OH)_3} i.e. boric acid or orthoboric acid, it does not ionize in water to give (H+)({H^ + }) ions. Hence it is not a protonic acid. As it accepts a pair of electrons from hydroxide ions so it is a lewis acid. The reaction is given below:
B(OH)3+2H2O→[B(OH4)]−(aq)+H3O+B{(OH)_3} + 2{H_2}O \to {[B(O{H_4})]^ - }(aq) + {H_3}{O^ + }
In case of PO(OH)3PO{(OH)_3}, i.e. H3PO4{H_3}P{O_4}, it ionizes in an aqueous solution mostly to give a combination of its three anions as:
H3PO4+H2O⇆H3O++H2PO4− H2PO4−+H2O⇆H3O++HPO42− HPO42−+H2O⇆H3O++PO43−  {H_3}P{O_4} + {H_2}O\underset {} \leftrightarrows {H_3}{O^ + } + {H_2}PO_4^ - \\\ {H_2}PO_4^ - + {H_2}O\underset {} \leftrightarrows {H_3}{O^ + } + HPO_4^{2 - } \\\ HPO_4^{2 - } + {H_2}O\underset {} \leftrightarrows {H_3}{O^ + } + PO_4^{3 - } \\\
Hence it is also a protonic acid.
For the case of SO(OH)2SO{(OH)_2}i.e. H2SO3{H_2}S{O_3}, in aqueous solution it dissociates as:
H2SO3+H2O→H3O++HSO3− HSO3−+H2O→H3O++SO32−  {H_2}S{O_3} + {H_2}O \to {H_3}{O^ + } + HSO_3^ - \\\ HSO_3^ - + {H_2}O \to {H_3}{O^ + } + SO_3^{2 - } \\\
Hence, it is also a protonic acid.
Hence the correct answers are A, C, D.

Note: The concept of protonic acid is given by both Arrhenius and Bronsted. Since in the case of the protic solvent, there are O-H or N-H bonds which form a hydrogen bond with themselves. These O-H or N-H bonds serve as a source of proton donors. Also, as we know H+{H^ + }ion is nothing but a proton, which is not capable of independent existence, so it exists as hydronium ion (H3O+)({H_3}{O^ + }).