question_answer

What is \[[{{H}^{+}}]\] in mol/L of a solution that is 0.20 M in \[C{{H}_{3}}COONa\] and 0.10 M in \[C{{H}_{3}}COOH\]? (\[{{K}_{a}}\]for \[C{{H}_{3}}COOH=1.8\times {{10}^{-5}}\])     [AIPMT (S) 2010]

A)  \[3.5\times {{10}^{-4}}\]        

B)       \[1.1\times {{10}^{-5}}\]

C)  \[1.8\times {{10}^{-5}}\]        

D)       \[9.2\times {{10}^{-6}}\]

Correct Answer: D

Solution :

Key Idea (weak acid) and (conjugated salt) form acidic buffer and for acidic buffer,

and

Now,