Question

The pH of 0.1 M aqueous solution of NaCl, and will follow the order:
a.) NaCl < \[\,C{H_3}COONa\] < \[N{H_4}Cl\]
b.) \[N{H_4}Cl\] < NaCl < \[\,C{H_3}COONa\]
c.) \[N{H_4}Cl\] < \[\,C{H_3}COONa\] < NaCl
d.) NaCl < \[N{H_4}Cl\] < \[\,C{H_3}COONa\]

Answer 1

Hint: pH of a solution accounts for the free \[{H^ + }\] ions available in the solution. It is a scale used to determine the acidity or basicity of an aqueous solution. A weak acid is a substance that partially dissociates when dissolved in a solvent.

Complete step by step answer:
pH of a solution is a scale used to specify the acidity or basicity of an aqueous solution. It is known as the potential of hydrogen. Lower pH values correspond to solutions which are more acidic in nature, while higher values correspond to solutions which are more basic in nature. If the pH of a solution < 7, it is acidic. If the pH of a solution = 7, it is neutral and if the pH > 7, it is basic. The pH of a solution is defined as the negative of logarithm of the molar concentration of hydrogen ions in the solution. Mathematically,
pH = - log[\[{H^ + }\]]

Now, a weak acid may be defined as an acid that partially dissociates into its constituent ions in an aqueous solution or water. In contrast, a strong acid fully dissociates into its ions in water. The strength of an acid is judged based on its degree of dissociation. Higher the degree of dissociation/ionization of an acid, higher is its ionization and the better acid it is.
In the given question, NaCl ionizes completely resulting in a neutral solution.
\[NaCl \to N{a^ + } + C{l^ - }\]
\[C{l^ - }\] does not combine further to form hydrochloric acid as it is a strong acid. Hence, it is a neutral salt and its pH is 7.
\[\,C{H_3}COONa \to N{a^ + } + C{H_3}CO{O^ - }\]
Acetate ion further reacts with water to produce hydroxide ion.
\[C{H_3}CO{O^ - } + {H_2}O \to C{H_3}COOH + O{H^ - }\]
Thus, pH > 7.
\[N{H_4}Cl \to N{H_4}{^ + } + C{l^ - }\]
Ammonium ions further react with water to produce hydrogen ions.
\[N{H_4}{^ + } + {H_2}O \to N{H_4}OH + {H^ + }\]
Thus, pH < 7.

Hence, the correct answer is (B) \[N{H_4}Cl\] < NaCl < \[C{H_3}CO{O^ - }\]

Note: Remember that only ions which further react with water are the ones which produce a weak acid or a weak base. Strong acids or strong bases are not formed by reaction with water.