Question

If the $pK_a$ of acetic acid and $pK_b$ of dimethylamine are $4.76$ and $3.26$ respectively, the pH of dimethyl ammonium acetate solution is

• A. 7.75
• B. 6.75
• C. 7
• D. 8.5

Answer 1

Answer: (A)

7.75

Answer 2

$pH =7+\frac{1}{2}\left[ p K_{a}- p K_{b}\right]$

Here, $p K_{a}=4.76, p K_{b}=3.26$

$=7+\frac{1}{2}[4.76-3.26]$

$=7+\frac{1}{2}[1.50]$

$=7+0.75=7.75$