Question

The pH of ${\text{0}}{\text{.1}}$ M solution of the following salts increases in the order of:
A.$NaCl\, < N{H_4}Cl\, < \,NaCN\, < \,HCl$
B.$HCl\, < N{H_4}Cl\, < \,NaCl\, < \,NaCN$
C.$NaCN\, < N{H_4}Cl\, < \,NaCl < \,HCl$
D.$HCl\, < NaCl\, < \,NaCN\, < \,N{H_4}Cl$

Answer 1

Salts are made up of acid and base so, we will hydrolysis the salts and check its components. Salt which is made up of strong acid will have low pH. Salt which is made up of weak acid will have high pH. The base neutralized the acid.

Complete step-by-step answer:
The formula of pH is as follows:
${\text{pH}}\, = \, - \log \,\left[ {{{\text{H}}^{\text{ + }}}} \right]$
pH is the negative logarithm of hydrogen ion concentration. As the hydrogen ion concentration increases the pH decreases. Hydrogen ion concentration depends upon the dissociation of the acid. More will be the dissociation of acid more will be hydrogen ion concentration. The Stronger the dissociation the acid will be.
The given salts are, ${\text{NaCl}}$,$\,{\text{N}}{{\text{H}}_{\text{4}}}{\text{Cl}}\,$,${\text{NaCN}}$and $\,{\text{HCl}}$.

We will hydrolyze the given salts to determine the acid and base from which the salts are prepared.
${\text{NaCN}}\,\,{\text{ + }}\,{{\text{H}}_{\text{2}}}{\text{O}}\,\, \to \,{\text{NaOH}}\,{\text{ + }}\,{\text{HCN}}$

Sodium cyanide salt is made up of base sodium hydroxide and acid hydrogen cyanide. The hydrogen cyanide is a weak acid so its pH will be highest.
${\text{NaCl}}\,\,{\text{ + }}\,{{\text{H}}_{\text{2}}}{\text{O}}\,\, \to \,{\text{NaOH}}\,{\text{ + }}\,{\text{HCl}}$

Sodium chloride salt is made up of base sodium hydroxide and hydrochloric acid. The hydrochloric acid is a strong acid and sodium hydroxide is also a strong base, so the base completely neutralizes the acid. So, the solution will be neutral.

${\text{N}}{{\text{H}}_4}{\text{Cl}}\,\,{\text{ + }}\,{{\text{H}}_{\text{2}}}{\text{O}}\,\, \to \,{\text{N}}{{\text{H}}_4}{\text{OH}}\,{\text{ + }}\,{\text{HCl}}$
Ammonium chloride salt is made up of base ammonium hydroxide and hydrochloric acid. The hydrochloric acid is a strong acid but ammonium hydroxide is a weak strong base, so the base does not neutralize the acid completely. So, the ammonium chloride salt solution will have more acid than the sodium chloride salt solution so, the pH of ammonium chloride salt will be lower than the sodium chloride salt.

Hydrogen chloride is a strong acid, so its pH will be lowest. So, the pH of ${\text{0}}{\text{.1}}$M solution of the following salts increases in the order of ${\text{HCl}}\,{\text{ < N}}{{\text{H}}_{\text{4}}}{\text{Cl}}\,{\text{ < }}\,{\text{NaCl}}\,{\text{ < }}\,{\text{NaCN}}$.

Therefore, option (B)${\text{HCl}}\,{\text{ < N}}{{\text{H}}_{\text{4}}}{\text{Cl}}\,{\text{ < }}\,{\text{NaCl}}\,{\text{ < }}\,{\text{NaCN}}$, is correct.

Note: Acidity tells the acidic strength of the acids. Acidity is inversely proportional to the pH. As the pH increases the basic character increases. pH scale represents the acidity or basicity value range form $0 - 14$. The pH range of $0 - 6$ represents an acid. As the pH increases from$0$to$6$, the acidity decreases. The pH value $7$represents the neutral substance. The pH range of $8 - 14$ represents a base. As the pH increases from$8$to$14$, the basicity increases.