Question

A strong acid and a weak base reacts to form a salt. What will be the pH value of this salt in aqueous solution?

• A. pH = 7
• B. pH > 7
• C. pH < 7
• D. Variable pH, may be less or more than 7 at a particular instance

Answer 1

The correct option is C pH < 7

A strong acid and a weak base reacts to form an acidic salt. When the salt undergoes hydrolysis, the weak base is partially ionised whereas the strong acid ionises completely.
This results in an increase in the concentration of ${\text{H}}^{+}$ ions which makes the solution acidic. The pH of such solutions are less than 7.
For example:

$\text{HCl (aq)}+{\text{NH}}_4\text{OH (aq)}\to {\text{NH}}_4\text{Cl (aq)}+{\text{H}}_2\text{O (l)}$

Here, $\text{HCl}$ and ${\text{NH}}_4\text{OH}$ are the strong acid and weak base respectively.