The pH of an aqueous solution containing 1M benzoic acid ( pK _ a =...

$\begin{cases} & Benzoicacid & + & Sodiumbenzoate & \\ Molarity & 1M & & 1M & \\ Volume & {V}_{a}ml & & {V}_{s}ml & \\ millimoles & {V}_{a} \times 1 & & {V}_{s} \times 1 & \\ & & & & \end{cases}$

$pH = 4 . 5$

${pK}_{a} = 4 . 20$

$pH = {pK}_{a} + log\dfrac{[ \text{salt} ]}{[ \text{acid} ]}$

$4 . 5 = 4 . 2 + \log \left(\dfrac{{V}_{s}}{{V}_{a}}\right)Where, {V}_{s} - Volumeofsalt{V}_{a} - Volumeofacid$

$\dfrac{{V}_{s}}{{V}_{a}} = 2$..........(i)

${V}_{s} + {V}_{a} = 300$........(ii)

${V}_{a} = 100ml$