Question

100 mL of 0.02 M benzoic acid $(p{K}_a=4.2)$ is titrated using 0.02 M NaOH. pH after 50 mi, and 100 mL of NaOH have been added are

• A. 3.50, 7
• B. 4.2, 7
• C. 4.2, 8.1
• D. 4.2, 8.25

Answer 1

The correct option is C 4.2, 8.1

C. $4.2,8.1$

Formula,

$pH=pKa+\log \frac{salt}{acid}$

$=4.2+\log \frac{0.001}{0.001}$

$\therefore pH=4.2$......................I

$pH=7+\frac{1}{2}[pKa+\log C]$

$=7+\frac{1}{2}[4.2+\log 0.01]$

$=7+\frac{1}{2}\left[\frac{4.2}{2}\right]$

$=7+\frac{1}{2}\left[2.2\right]$

$=8.1$.............................II