Question

Explain, "orthophosphoric acid, H₃PO₄ is tribasic but phospharus acid, H₃PO₃ is dibasic".

Answer 1

Basicity = number of replaceable hydrogen (or H atoms attached to O atom)

Structure of orthophosphoric acid (H₃PO₄) and phosphorus acid (H₃PO₃) shows the presence of 3 and 2 replaceable hydrogen atoms respectively. Hence, the basicity of H₃PO₄ is 3 (ie, tribasic) and that of H₃PO₃ is 2 (ie, dibasic).