Question

Which one of the following is acid salt?

• A. ${\mathrm{Na}}_2\mathrm{S}$
• B. ${\mathrm{Na}}_2{\mathrm{SO}}_3$
• C. ${\mathrm{NaHSO}}_3$
• D. ${\mathrm{Na}}_2{\mathrm{SO}}_4$

Answer 1

The correct option is C

${\mathrm{NaHSO}}_3$

Explanation for the correct option

(C) ${\mathbf{NaHSO}}_{\mathbf{3}}$

Acids

• According to Arrhenius's theory, acids are species that dissociate in water to produce hydrogen ions $\left({\mathrm{H}}^{+}\right)$.
• According to Brönsted-Lowry theory, an acid is a substance that can donate a hydrogen ion $\left({\mathrm{H}}^{+}\right)$.
• Consider the dissolution of ammonia $\left({\mathrm{NH}}_3\right)$ in water $\left({\mathrm{H}}_2\mathrm{O}\right)$, which is described by the following equation:

• According to Lewis's acid-base concept, acid is a species that takes an electron pair.
• Lewis acids can be electron-deficient entities such as ${\mathrm{AlCl}}_3,{\mathrm{Co}}^{3+}$, and ${\mathrm{Mg}}^{2+}$.
• It has also been proven that strong acids have weak conjugate bases and vice versa.
• A strong base has a weak conjugate acid and vice versa.

${\mathbf{NaHSO}}_{\mathbf{3}}$

• Sodium bisulfite $\left({\mathrm{NaHSO}}_3\right)$ dissociation reaction is as follows:

${\mathrm{NaHSO}}_3\rightleftharpoons {\mathrm{Na}}^{+}+{\mathrm{HSO}}_3^{-}$

• ${\mathrm{NaHSO}}_3$, can still has protons that can be donated.
• Its anion can act as an acid by releasing one more proton, making it acidic by nature.

Explanation for incorrect options

(A) ${\mathbf{Na}}_{\mathbf{2}}\mathbf{S}$

• ${\mathrm{Na}}_2\mathrm{S}$ is basic in nature because it is a weak acid-strong base salt.

(B) ${\mathbf{Na}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{3}}$

• ${\mathrm{Na}}_2{\mathrm{SO}}_3$ is basic in nature because it is a weak acid-strong base salt.

(D) ${\mathbf{Na}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$

• ${\mathrm{Na}}_2{\mathrm{SO}}_4$ is neutral by nature because it is a strong acid-strong base salt.

Therefore, the correct option is (C) ${\mathbf{NaHSO}}_{\mathbf{3}}$.