Question

Fixed volume of 0.1 M benzoic acid (pK_a = 4.2) solution is added into 0.2 M sodium benzoate solution and formed a 300 ml, resultant acidic buffer solution. If pH of this buffer solution is 4.5 then find added volume of benzoic acid –

• A. 100 ml
• B. 150 ml
• C. 200 ml
• D. None of these

Answer 1

Answer: (C)

200 ml

Answer 2

Ph = pK_a­ + $\frac { \log \left[ \mathrm { C } _ { 6 } \mathrm { H } _ { 5 } \mathrm { COO } ^ { - } \right] } { \left[ \mathrm { C } _ { 6 } \mathrm { H } _ { 5 } \mathrm { COOH } \right] }$

$\therefore \frac { \left[ \mathrm { C } _ { 6 } \mathrm { H } _ { 5 } \mathrm { COO } ^ { - } \right] } { \left[ \mathrm { C } _ { 6 } \mathrm { H } _ { 5 } \mathrm { COOH } \right] }$ = 2

Let volume of acid is V ml.

= 2

Ž V = 200 ml.