Question

0 ml of 0.1M ammonia is mixed with 20 ml 0.1M HCl. What is the pH of the mixture? (pK_b for ammonia is 4.74).

(a) 4.74
(b) 2.26
(c) 9.26
(d) 5.00

Answer 1

Correct option is (c) 9.26

40 ml of 0.1M NH₃ solution

= 40 x 0.1 milli = 4 millimol

20 ml of 0.1 M HCl = 20 x 0.1 = 2 millimol

2 millimol of HCl neutralise 2 millimol of NH₄OH, to form 2 millimol of NH₄OH.

NH₄OH left = 2 millimol

Total volume = 60 ml