Question

1 M NH₄OH and 1 M HCl are mixed to make total volume of 300 mL. If pH of the mixture is 9.26 and pK_a (NH₄⁺) = 9.26 then volume ratio of NH₄OH and HCl will be:

(a) 1 : 1 

(b) 1 : 2

(c) 2 : 1 

(d) 3 : 1

Answer 1

Correct option: (c) 2 : 1

Explanation: 

HCl will convert equivalent amount of NH₄OH into NH₄Cl and thus resultant mixture is a buffer.

Let HCl = x mL NH₄Cl formed = x milli mol

NH₄OH = (300 – x) mL, NH₄OH left = (300 – 2x) milli mol

x = 100 mL = volume of HCl

200 mL = volume of NH₄OH