Question

What is the equivalent weight of ${H_3}P{O_2}$ ?

Answer 1

Hint : Equivalent weight of any substance is defined as the number of parts by weight of a given element which combines or displaces 1 part by weight of hydrogen, 8 part of oxygen, or 35.5 parts of weight of chlorine.

Complete Step By Step Answer:
Equivalent weight of acid are defined in terms of basicity. Basicity of the acid is defined as the total number of replaceable hydrogen ions present in any acid.
As we know that ${H_3}P{O_2}$ is known as hypophosphorous acid, therefore the equivalent of this acid is expressed in terms of the basicity of it.
Formula to calculate the equivalent weight of acid is-
$Eq = \dfrac{M}{n}$
Where, $Eq$ is equivalent weight of an acid
$M$ Is molecular weight of acid
$n$ Is basicity of acid
In order to calculate the equivalent weight of acid, first calculate its molecular mass.
Molecular mass of ${H_3}P{O_2}$ = molecular mass of hydrogen + molecular mass of phosphorus + molecular mass of oxygen.
Molecular mass of ${H_3}P{O_2} = \left( {3 \times 1} \right) + \left( {31} \right) + \left( {2 \times 16} \right)$
Molecular mass of ${H_3}P{O_2} = 3 + 31 + 32$
Molecular mass of ${H_3}P{O_2} = 66$
Hypophosphorous acid has the tendency to lose only one hydrogen atom because the remaining two hydrogen atoms are directly bonded with phosphorus atoms and do not participate in reaction.
Due to this reason hypophosphorous acid with value of $\left( n \right)$ is $1$ .
On substituting the values in formula of equivalent weight we get,
$Eq = \dfrac{{66}}{1}$
After solving this equation, we get that the equivalent weight of ${H_3}P{O_2}$ is $66$ .

Note :
Value of equivalent weight may vary in specific chemical reactions where more than one hydrogen atom of acid participated in the reaction. For example, when hypophosphorous acid undergoes a chemical reaction to form phosphine and phosphoric acid, oxidation value of acid changes and equivalent weight become $\left( {\dfrac{{3M}}{4}} \right)$ .