The pK b of dimethylamine and pK a of acetic acid are 3.27 and 4.77 respectively at T ( K ). The correct option for the pH of dimethylammonium acetate solution is :

Question

The pK b of dimethylamine and pK a of acetic acid are 3.27 and 4.77 respectively at T ( K ). The correct option for the pH of dimethylammonium acetate solution is : (A) 8.50 (B) 5.50 (C) 7.75 (D) 6.25

Tardigrade Admin · Accepted Answer

For a salt of weak acid and weak base PH does not depend on concentration of salt. P H =7+(1/2)[ P k a - P K b ] =7+(1/2)[4.77-3.27]=7.75

Q. The $p K_{b}$ of dimethylamine and $p K_{a}$ of acetic acid are $3.27$ and $4.77$ respectively at $T (K)$ . The correct option for the $p H$ of dimethylammonium acetate solution is :

$8.50$

$5.50$

$7.75$

$6.25$

For a salt of weak acid and weak base $P^{H}$ does not depend on concentration of salt.
$P^{H} = 7 + \frac{1}{2} [P^{k_{a}} - P^{K_{b}}]$
$= 7 + \frac{1}{2} [4.77 - 3.27] = 7.75$

Q. The pKb​ of dimethylamine and pKa​ of acetic acid are 3.27 and 4.77 respectively at T(K). The correct option for the pH of dimethylammonium acetate solution is :

8.50

5.50

7.75

6.25