Question

Find the number of dibasic oxy acids in the following.

$H_2CO_3, H_2SO_4, H_3PO_2, HPO_3, H_3BO_3$

Answer 1

2

Answer 2

To determine the basicity of an oxyacid, we need to identify the number of acidic hydrogen atoms present in its molecule. In oxyacids, the acidic hydrogen atoms are typically those bonded to oxygen atoms (-OH groups). Hydrogens bonded directly to the central atom (e.g., P-H bonds in phosphorus oxyacids) are generally not acidic. A dibasic oxyacid is one that can donate two protons ($H^+$ ions) per molecule.

Let's analyze each given oxyacid:

1. $H_2CO_3$ (Carbonic acid):

   • Structure: $O=C(OH)_2$
   • It has two -OH groups directly attached to the central carbon atom.
   • Basicity: 2 (dibasic)

2. $H_2SO_4$ (Sulfuric acid):

   • Structure: $O_2S(OH)_2$
   • It has two -OH groups directly attached to the central sulfur atom.
   • Basicity: 2 (dibasic)

3. $H_3PO_2$ (Hypophosphorous acid):

   • Structure: $H_2P(=O)OH$
   • It has one -OH group and two P-H bonds. Only the hydrogen atom attached to oxygen is acidic.
   • Basicity: 1 (monobasic)

4. $HPO_3$ (Metaphosphoric acid):

   • This acid typically exists as a polymer, $(HPO_3)_n$. Considering the simplest monomeric unit, its structure would be $O=P(H)OH$.
   • It has one -OH group and one P-H bond. Only the hydrogen atom attached to oxygen is acidic.
   • Basicity: 1 (monobasic)

5. $H_3BO_3$ (Boric acid):

   • Structure: $B(OH)_3$
   • Although it contains three -OH groups, boric acid acts as a Lewis acid, not a Brønsted-Lowry acid in the traditional sense. It accepts a hydroxide ion from water, thereby releasing a proton from the water molecule: $B(OH)_3 + H_2O \rightleftharpoons [B(OH)_4]^- + H^+$
   • It releases only one proton per molecule in aqueous solution.
   • Basicity: 1 (monobasic)

From the analysis, the dibasic oxyacids are $H_2CO_3$ and $H_2SO_4$. Therefore, the number of dibasic oxyacids in the given list is 2.