Question

For $H_{3}P{O}_3$ and $H_{3}P{O}_4$, the correct choice is:

• A. $H_{3}P{O}_3\text{is dibasic and non reducing}$
• B. $H_{3}P{O}_3\text{is dibasic and reducing}$
• C. $H_{3}P{O}_4\text{is tribasic and reducing}$
• D. $\text{None}$

Answer 1

The correct option is B $H_{3}P{O}_3\text{is dibasic and reducing}$

Basicity depends on the number of replaceable hydrogens. The hydrogen atoms which are directly attached to $O$ -atoms are replaceable hydrogens due to the greater electronegativity difference between oxygen and hydrogen atoms.

So, the basicity of $H_{3}P{O}_4$ is 3 and the basicity of $H_{3}P{O}_3$ is 2.

In $H_{3}P{O}_3$, the oxidation state of $P$ is +3. So, it can get further oxidised and accordingly can act as a reducing agent. But in $H_{3}P{O}_4$, the oxidation state of $P$ is +5, which is the the highest oxidation state for $P$ atom. Thus, $H_{3}P{O}_4$ is non reducing.