Question

2.5ML of 2/5M weak monoacidic base (K_b = 1 x 10^-12 at 25°C) is tirtrated with 2/15M HCl in water at 25°C. The concentration of H⁺ at equivalence point is (Kw = 1 x 10^-14 at 25°C)

(a) 3.7 x 10^-13M

(b) 3.2 x 10^-7M

(c) 3.2 x 10^-2M

(d) 2.7 x 10^-2M

Answer 1

The correct option (d)  2.7 x 10^-2M

Explanation:

Weak monoacidic base eg. BOH is neutralised as follows 

BOH + HCI → BCl+ H₂O 

At equivalence point all BOH gets converted into salt and remember! the coucentration of H⁺ (or pH of solution) is due to hydrolysis of resultant salt (BCl, cationic hydrolysis here)

(h should be estimated whether that can be neglected or not) on calculating h = 0.27 (significant. not negligible) 

[H⁺] = Ch = 0.1 x 0.27 = 2.7 x 10^-2M