Question

$pH$ of resultant solution formed by mixing equal volumes of two solutions having $pH=5.8$ and $pH=12.8$ is

• A. $12.5$
• B. $5.5$
• C. $6.1$
• D. $13.1$

Answer 1

The correct option is A $12.5$

$pH=12.8$
$\therefore pOH=1.2$
$\left[O{H}^{-}\right]={10}^{-1.2}$
$pH=5.8$
$\therefore \left[H^{+}\right]={10}^{-5.8}$
${10}^{-5.8}<<{10}^{-1.2}$
by mixing these two solutions, there will be very less change in $pH$ and therefore acid is added, so $pH$ will be decreased by a very small value.
So net $pH$ of final solution is around $12.5$