Question

Which one of the following salt’s aqueous solution is likely to have $pH < 7$ ?
A. $C{H_3}COON{H_4}$
B. NaCl
C. $N{H_4}Cl$
D. $C{H_3}COOK$

Answer 1

pH is defined as the negative logarithm of ${H^ + }$ ion. Now, there is a tool known as pH scale which ranges from 0-14. The solutions having a value of pH ranging from 0-7 on pH scale are termed as acidic and for the value from 7-14 are known as basic.

Complete step by step answer:
pH basically refers to the power of hydrogen. It is a measure of concentration of hydrogen ions, the acidity or alkalinity of a solution. Further, the pH scale is normally between 0-14. The aqueous solutions with a pH less than 7 are acidic and with a pH greater than 7 are basic or alkaline solutions. Now, let’s consider each option and then determine the correct one.
Option A i.e. $C{H_3}COON{H_4}$ is a salt of weak acid $C{H_3}COOH$ and weak base $N{H_4}OH$ . So, it is a neutral solution with pH value between 7-7.5.
NaCl is a salt of strong acid HCl and strong base NaOH? Again, it is also neutral with pH value between 7-7.5.
In the third option, i.e. $N{H_4}Cl$ , it is a salt of strong acid HCl and weak base $N{H_4}OH$ . So, it is an acidic solution with pH less than 7.
In the last option, i.e. $C{H_3}COOK$ , it is a salt of weak acid $C{H_3}COOH$ and strong base KOH. So, it is a basic solution with pH greater than 7.
Therefore, it is clear that the salt solution of $N{H_4}Cl$ is likely to have $pH < 7$ .

Hence, option C is correct.

Note: You should always remember that the pH of strong acid or base does not depend on temperature. Moreover, pH of weak acid decreases with increase in temperature due to increase in ionization and the pH of weak base increases with increase in temperature due to increase in ionization or ion concentration.