Question

The $pH$ of a dilute solution of acetic acid was found to be $4.3$ The addition of a small crystal of sodium acetate will cause $pH$ to:

• A. become less than $4.3$
• B. become more than $4.3$
• C. remain equal to $4.3$
• D. unpredictable

Answer 1

Answer: (B)

become more than $4.3$

Adding a common ion prevents the weak acid or weak base from ionizing as much as it would without the added common ion. The common ion effect suppresses the ionization of a weak acid by adding more of an ion that is a product of this equilibrium.

Due to this common ion effect, when we add sodium acetate dissociation of acetic acid decreases and solution will have less number of hydrogen ion and so, pH increases. (as $pH=-log\left[H^{+}\right]$)