Question

The $pH$ of a solution is $7$. To this solution, sufficient base is added to increase the $pH$ to $12$. The increase in $\stackrel{⊝}{O}H$ ion concentration is:

• A. $5$ times
• B. $1000$ times
• C. ${10}^5$ times
• D. $4$ times

Answer 1

The correct option is C ${10}^5$ times

We know, $pH=-log\left[H^{+}\right]$

So at $pH=7$,

$\left[H^{+}\right]={10}^{-7}=\left[O{H}^{-}\right]$

At $pH=12$,

$\left[H^{+}\right]={10}^{-12};\left[O{H}^{-}\right]={10}^{-2}$

Therefore, increase in concentration of $\left[O{H}^{-}\right]={10}^5$ times.