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:

(1) 8.50

(2) 5.50

(3) 7.75

(4) 6.25

Answer 1

Correct option is (3) 7.75

Dimethylammonium acetate is a salt of weak acid and weak base whose pH can be calculated as

pH = 7 + \(\frac 12\)(pK_a − pK_b)

= 7 + \(\frac 12\)(4.77 − 3.27)

= 7 +  \(\frac 12\)(1.5)

= 7 + 0.75

= 7.75

Answer 2

Correct answer is (3).

Dimethylammonium acetate is a weak acid & weak base type of salt