pH of acid or base mixtures

Exercise 2

   

Determine the $pH$ of the solution obtained by mixing $V_1$ = 400 $mL \; NaOH $ 0.7 $M$ with $V_2$ = 150 $mL \; NaF $ 0.95 $M$

$OH^-$ : treated as a strong base , $F^-$ : weak base $n_{OH^-}$ $=$ $c_{OH^-}\cdot V_1$ = 0.28 mol $pH$ $=$ $14$ $+$ $log\frac{n_{OH^-}}{V_1+V_2}$ = 13.71