Question

Explain the following:

H₃PO₃ is not a tribasic acid.

Answer 1

H₃PO₃ is not a tribasic acid because in oxyacids of phosphorus, hydrogen atoms which are attached to oxygen atoms are replaceable. Hydrogen atoms directly bonded to phosphorus atoms are not replaceable.

\[\begin{array}{cc}
\ce{O}\phantom{..................}\\
||\phantom{..................}\\
\ce{P}\phantom{..................}\\
/\phantom{..}|\phantom{..}\backslash\phantom{...................}\\
\ce{\phantom{}HO\phantom{..}OH\phantom{..}H -> Not replaceable}
\end{array}\]