Question

What is the basicity of phosphorus acid (H₃PO₃)?

Answer 1

The basicity of phosphorus acid (H₃PO₃) is explained as follows:

1. Phosphorus acid contains two ionisable \[\ce{P - OH}\] bonds and one non-ionisable \[\ce{P - H}\] bond.
2. Only the \[\ce{P - OH}\] bonds contribute to the acid's basicity.
3. Since there are two ionisable \[\ce{P - OH}\] groups, the basicity of H₃PO₃ is dibasic.
4. The \[\ce{P - H}\] bond does not release H⁺ ions and thus does not affect basicity.

Hence, phosphorus acid (H₃PO₃) is dibasic because it has two ionisable acidic hydrogen atoms from \[\ce{P - OH}\] groups.