Determine the $pH$ of the solution obtained by mixing $V_1$ = 200 $mL$ 0.4 $M$ chlorhydric acid with enough phenol to increase the total volume upto $V_2$ = 50 $mL$. (Phenol $C_6H_5OH$ is a pink solid with density $1.0545$ ; it is a weak acid)
$HCl$: strong acid , $C_6H_5OH$: weak acid $n_{HCl}$ $=$ $c_{HCl}\cdot V_{HCl}$ = 0.08 $mol$ $pH$ $=$ $-log\frac{n_{HCl}}{V_2}$ = -0.204
