Question

A $100mL,0.1M$ solution of ammonium acetate is diluted by adding $100mL$ of water. The pH of the resulting solution will be $(p{K}_a$ of acetic acid is nearly equal o $p{K}_b$ of $N{H}_{4}OH)$ :

• A. $4.9$
• B. $5.0$
• C. $7.0$
• D. $10.0$

Answer 1

Answer: (C)

$7.0$

Ammonium acetate is a salt of weak acid and weak base. When solutions of such salts diluted resulting pH of solution is calculated from following relationship

$pH=7+\frac{1}{2}p{K}_a-\frac{1}{2}p{K}_b$

$\because p{K}_a\simeq p{K}_b$ (given)

$\therefore pH$ of diluted solution $=7$