pH of a mixture of 1 M benzoic acid ( pK a =4.20) and 1 M C 6 H 5 COONa is 4.5, what is the volume of benzoic acid required to prepare a 300 ml buffer [ log 2=0.3] ?

Question

pH of a mixture of 1 M benzoic acid ( pK a =4.20) and 1 M C 6 H 5 COONa is 4.5, what is the volume of benzoic acid required to prepare a 300 ml buffer [ log 2=0.3] ? (A) 200 ml (B) 150 ml (C) 100 ml (D) 50 ml

Tardigrade Admin · Accepted Answer

pH = pKa + log ( V /300- V ) 4.5=4.2+ log ( V /300- V ) 0.3= log ( V /300- V ) log 2= log ( V /300- V ) ∴ 2=( V /300- V ) ∴ V =200 ∴ Volume of the acid =300-200=100

Q. $p H$ of a mixture of $1 M$ benzoic acid $(p K_{a} = 4.20)$ and $1 M C_{6} H_{5} COON a$ is $4.5$ , what is the volume of benzoic acid required to prepare a $300 m l$ buffer $[lo g 2 = 0.3]$ ?

200 ml

150 ml

100 ml

50 ml

$p H = p K a + lo g \frac{V}{300 - V}$
$4.5 = 4.2 + lo g \frac{V}{300 - V}$
$0.3 = lo g \frac{V}{300 - V}$
$lo g 2 = lo g \frac{V}{300 - V}$
$∴ 2 = \frac{V}{300 - V}$
$∴ V = 200$
$∴$ Volume of the acid $= 300 - 200 = 100$

Q. pH of a mixture of 1M benzoic acid (pKa​=4.20) and 1MC6​H5​COONa is 4.5, what is the volume of benzoic acid required to prepare a 300ml buffer [log2=0.3] ?