Question

The equivalent weight of ${{H}_{3}}P{{O}_{2}}$ , when it disproportionate into $P{{H}_{3}}\text{ and }{{\text{H}}_{3}}P{{O}_{4}}$ is,
(A) 82
(B) 61.5
(C) 33
(D) 49.5

Answer 1

Hint: As we know that in a chemical reaction the equivalence of a substance is explained as the amount of which combines with 1 mole of the hydrogen atoms or replaces the same number of hydrogen atoms in the reaction. Thus equivalent weight in grams is the weight of 1 grams.

Complete step by step solution:
In this question we have to find the ${{H}_{3}}P{{O}_{2}}$ disproportionate and form $P{{H}_{3}}$. We can write the equation involved as follow:
$\begin{align}
& {{H}_{3}}P{{O}_{2}}\to P{{H}_{3}} \\
& {{P}^{+}}+4{{e}^{-}}\to {{P}^{3-}} \\
\end{align}$
The equivalent weight of ${{H}_{3}}P{{O}_{2}}$ can be calculated by dividing the ratio of molecular weight to the valence factor =$\dfrac{M}{4}$
Again ${{H}_{3}}P{{O}_{2}}$dissociates and form ${{H}_{3}}P{{O}_{3}}$this reaction is mentioned below:
$\begin{align}
& {{H}_{3}}P{{O}_{2}}\to {{H}_{3}}P{{O}_{3}} \\
& {{P}^{+}}-2{{e}^{-}}\to {{P}^{3+}} \\
\end{align}$
The equivalent weight of ${{H}_{3}}P{{O}_{2}}$ can be calculated by dividing the ratio of molecular weight to the valence factor=$\dfrac{M}{2}$
The molar mass of ${{H}_{3}}P{{O}_{2}}$ is 66g/mol
Now the equivalent weight will be $\dfrac{M}{4}+\dfrac{M}{2}=16.5+33$= 49.5

Hence the correct answer is option (D).

Additional information:
We know that the law of equivalence is one equivalence of an element combined with one equivalence of others. Equivalent weight of an acid in an acid base reaction is the portion of weight of 1 mole of the acid that can furnish 1 mole of hydrogen ions.

Note: As we know that a redox reaction that reactant is transformed into products by simultaneous reduction reaction as well as the oxidation reaction is termed as the disproportionation reaction. For s reaction say that hydrogen peroxide transformed into water and oxygen. In this reaction hydrogen peroxide oxidizes to form oxygen and it reduces and forms water.