Question

Which of the following is not an acidic salt?

A.${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_{\text{2}}}$
B.${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_3}$
C.${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_4}$
D.All of these

Answer 1

Any salt that has replaceable hydrogen atoms is known as an acidic salt. The aqueous solutions of acidic salts turn blue litmus red. Thus, the aqueous solutions of acidic salts are acidic in nature.

Step by step answer:
The salt ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_{\text{2}}}$ is formed by the neutralization of weak acid ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{2}}}$ and strong base ${\text{NaOH}}$.
The structure of ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{2}}}$ is as follows:

Thus, ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{2}}}$ has only one replaceable hydrogen atom. This one hydrogen atom is replaced by one sodium atom and ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_{\text{2}}}$ is formed.
Thus, ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_{\text{2}}}$ is not an acidic salt.
Thus, option (A) is correct.
The salt ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_3}$ is formed by the neutralization of weak acid ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_3}$ and strong base ${\text{NaOH}}$.
The structure of ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_3}$ is as follows:

Thus, ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_3}$ has two replaceable hydrogen atom. One hydrogen atom is replaced by one sodium atom and ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_3}$ is formed. One replaceable hydrogen atom is still remaining.
Thus, ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_3}$ is an acidic salt.
Thus, option (B) is not correct.
The salt ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_4}$ is formed by the neutralization of weak acid ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$ and strong base ${\text{NaOH}}$.
The structure of ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$ is as follows:

Thus, ${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_4}$ has three replaceable hydrogen atom. One hydrogen atom is replaced by one sodium atom and ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_4}$ is formed. Two replaceable hydrogen atoms are still remaining.
Thus, ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_4}$ is an acidic salt.
Thus, option (C) is not correct.
Thus, ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_{\text{2}}}$ is not an acidic salt.

Thus, the correct option is (A). ${\text{Na}}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_{\text{2}}}$.

Note: In the acids, the hydrogen atoms that are attached to the oxygen atom are known as replaceable hydrogen atoms. Hydrogen atoms attached to phosphorus directly are not replaceable.