question_answer

20 mL of 0.2 M \[NaOH\] is added to 50 mL of 0.2 M acetic acid. The pH of this solution after mixing is \[({{K}_{a}}=1.8\times {{10}^{-5}})\]

A)  \[4.5\]              

B)  \[2.3\]

C)  \[3.8\]              

D)  \[4\]

Correct Answer: A

Solution :

  \[pH=-\log (1.8\times {{10}^{-5}})+\log \frac{4/70}{6/70}\] \[=4.56\]