Question

Which of the following salts will dissolve in water to produce a solution having a pH below 7?

• A. $\mathrm{AgCl}$
• B. $\mathrm{KCl}$
• C. ${\mathrm{NH}}_4\mathrm{Cl}$
• D. $\mathrm{HCl}$

Answer 1

The correct option is C

${\mathrm{NH}}_4\mathrm{Cl}$

Explanation for the correct option:

• The phenomenon of the interaction of any salt with the H+ and OH- ions of water is called salt hydrolysis.
• Depending upon the nature of the acid and base produced when salt reacts with water, the salts are classified into 4 types:

1. Salts of strong acid and strong base.
2. Salt of a weak acid and strong base.
3. Salt of strong acid and weak base.
4. Salts of a weak acid and weak base.

• Among the given options, option (C).${\mathrm{NH}}_4\mathrm{Cl}$ (Ammonium chloride) is a salt formed from a weak base ${\mathrm{NH}}_4\mathrm{OH}$(Ammonium hydroxide) and a strong acid $\mathrm{HCl}$(Hydrochloric acid). the pH will be less than 7 since such solution will be acidic in nature.

Explanation for the incorrect option:

• (A) $\mathrm{AgCl}$(Silver chloride) salt do not dissolve in water so, it is incorrect option.
• (B) $\mathrm{KCl}$(Potassium chloride) is the salt of a strong acid and strong base, When they undergo hydrolysis, it forms neutral solution, with pH equal to 7. Therefore, this option is incorrect.
• When $\mathrm{HCl}$(Hydrogen chloride) dissolves in water, it dissociates into ${\mathrm{H}}^{+}$ and ${\mathrm{Cl}}^{-}$ ions. $\mathrm{HCl}$ is a strong acid and not a salt.

Hence, the option (C) ${\mathrm{NH}}_4\mathrm{OH}$ is correct. The salts that will dissolve in water to produce a solution having a pH below 7 is ${\mathrm{NH}}_4\mathrm{OH}$ and $\mathrm{HCl}$.