Question

What is the Equivalent mass of $H_{3}P{O}_3$ in the following reaction?
$H_{3}P{O}_3\to H_{3}P{O}_4+P{H}_3$

• A. $\frac{M}{2}$
• B. $\frac{M}{6}$
• C. $\frac{2M}{3}$
• D. $\frac{3M}{2}$

Answer 1

The correct option is C $\frac{2M}{3}$

$4H_3\stackrel{+3}{P}{O}_3\to 3H_3\stackrel{+5}{P}{O}_4+\stackrel{-3}{P}{H}_3$

This is a disproportionation reaction.

Equivalent mass of oxidant/reductant = sum of equivalent mass of true half reaction

$\text{Equivalent mass}=\frac{\text{molarity}}{\text{change in oxidation state}}$
$\therefore$
Equivalent mass of $H_{3}P{O}_3=\frac{M}{2}+\frac{M}{6}=\frac{2M}{3}$