Question

The pH of a solution is $7.00$. To this solution, sufficient base is added to increase the pH to $12.0$. The increase in ${OH}^{-}$ 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

As we know,

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

So at pH = 7,

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

At pH = 12,

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

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

Hence, correct is option C.